Let us talk about some of the Fiqh points that I was asked about and they are really the top questions that I got on this matter.
DOES ONE HAVE TO DO ALL TEN DAYS?

He can do a portion of them. Let us say he has a job, he goes for five days and then suddenly they call him to work. He will get the five days of reward Inshaa Allah and then when he finishes what he has to do, he comes back and initiates the Niyyah for a new I’tikaaf. The best is to do all ten days but if one does a few days or even if it is as short as five minutes, that is acceptable.
Ash-Shaafi’ee said on this matter you are your own Ameer (leader), it is what you choose. You can continue or you can leave it whenever you want, there is no sin in it. In Fath Al-Baari, Ibn Hajr said as long as one did not do a Nathr (نذر) (meaning a vow), he can break his I’tikaaf and resume if he wishes. What we mean by a vow is if someone says O Allah if you grant me this, I am going to do ten days of I’tikaaf or three days of I’tikaaf. If he does that vow, the vow becomes a Fardh upon him and he must do it as he says.

WHAT IS THE MINIMUM DURATION OF I’TIKAAF?

The Hanaabilah said it is a portion of a day (a portion of a day is sufficient). The Hanafiyyah said any time is sufficient. The Shaafi’iyyah said the length of the duration that one spends in Rukoo’. The one, two or three minutes that you spend in Rukoo’ is sufficient a time for I’tikaaf. Once you enter the Masjid with the Niyyah of I’tikaaf, that is I’tikaaf. It could be for three minutes, for one day, for two days or for a month. The ones that limited were the Maalikiyyah who limited it for a day and a night, but really it is what the three Imaams indicated (that there is no time limit and it could be any minimum amount of time you spend in a Masjid).
When I was a child we used to go to the Masjid of the Prophet sallallahu ‘alayhi wa sallam. I used to memorise the Qur’an and that is where I memorised the Qur’an. We used to go there every single night for four and a half years, from ‘Asr until Ishaa’. I remember we did not miss a single day except one day when the Masjid flooded, because back then they did accommodate well for when it rained severely. When we would go into the Masjid from ‘Asr to Ishaa’, my father would always remind me and say when you enter the Masjid have the intention in your heart to do I’tikaaf. If you go in a Masjid from Maghrib to Ishaa’ and you make the intention of I’tikaaf, you get the Ajr (reward) of it. Two people can enter the same Masjid at the same time and leave at the same time, one of them gets the reward of I’tikaaf and one does not. That is because one of them had the intention of I’tikaaf and the other did not.
However, to reap the full benefits of I’tikaaf that is when you go in seclusion and you sever yourself from the world. You leave your cell phone and everything behind you. You sever yourself from the worldly matters, unless there is something important. There is no problem with communicating in matters that are important.
From a Fiqh point of view, I’tikaaf is Sunnah. It is Sunnah and just like many think Taraweeh is only Sunnah throughout Ramadhaan, Taraweeh, Qiyaam and I’tikaaf are Sunnah throughout the year.

I’TIKAAF MUST BE IN A MASJID

Some say well if you want me to be alone, I will do I’tikaaf in my house by myself. For it to be I’tikaaf it has to be in a Masjid, that is a condition of it. The wives of the Prophet sallallahu ‘alayhi wa sallam did I’tikaaf in the Masjid. Had it been permitted to do so in their houses, the Prophet sallallahu ‘alayhi wa salam would have directed them to that.
Allah said:
وَلَا تُبَاشِرُ‌وهُنَّ وَأَنتُمْ عَاكِفُونَ فِي الْمَسَاجِدِ... ﴿البقرة: ١٨٧﴾
And do not have sexual relations with them (your wives) while you are in I’tikaaf (i.e. confining oneself in a mosque for prayers and invocations leaving the worldly activities) in the mosques. (Surat al-Baqarah: 187)
And He said:
...وَعَهِدْنَا إِلَىٰ إِبْرَاهِيمَ وَإِسْمَاعِيلَ أَن طَهِّرَا بَيْتِيَ لِلطَّائِفِينَ وَالْعَاكِفِينَ وَالرُّكَّعِ السُّجُودِ ﴿البقرة: ١٢٥﴾
And We commanded Ibraheem and Isma’eel that they should purify My House (the Ka’bah at Makkah) for those who are circumambulating it, or staying (I’tikaaf), or bowing or prostrating themselves (there, in prayer). (Surat al-Baqarah: 125)
Also, the I’tikaaf of the Prophet sallallahu ‘alayhi wa sallam was in the Masjid. I’tikaaf in a house is not permissible, not even for a woman. You can worship in your house but it is not I’tikaaf and it is not called I’tikaaf. In the fifteenth volume of his Fataawa, Ibn Taymiyyah said I’tikaaf for women is in the Masjid and they should stay away from the house.

SOME OF THE ETIQUETTES OF I’TIKAAF

Some of the etiquettes of I’tikaaf that one should know is that one should remain in the Masjid and not leave, unless it is an essential matter like using the bathroom. It is better to remain in the Masjid during I’tikaaf than to follow a Janaazah and you know how much reward there is in following a Janaazah (Qiraat of reward). It is better to remain in the Masjid than to visit someone who is ill. It is better to remain in the Masjid during I’tikaaf than to have relationship with a wife. Notice how these matters are encouraged and they have so much reward to them, but when you are doing I’tikaaf you are better off staying in the Masjid.
One can leave for essential matters like using the bathroom, taking a shower, getting clothes or maybe getting food and drink unless someone brings it. He should go bring the food and eat it in the Masjid. Do not go eat in a restaurant or at home, unless you are unable to do so in the Masjid. One can speak to and talk to his family or visitors as the Prophet sallallahu ‘alayhi wa sallam did with Safiyyah. If you bring your cell phone, make sure you only use it for essential matters. Especially the sisters, they may need it to remain in contact with their families but keep it for only essential matters.

WHAT INVALIDATES I’TIKAAF?

One being an apostate (Nas’alullah as-Salaamah), women on their days, sexual relationship and leaving the Masjid for no need.
وَلَا تُبَاشِرُ‌وهُنَّ وَأَنتُمْ عَاكِفُونَ فِي الْمَسَاجِدِ... ﴿البقرة: ١٨٧﴾
And do not have sexual relations with them (your wives) while you are in I’tikaaf (i.e. confining oneself in a mosque for prayers and invocations leaving the worldly activities) in the mosques. (Surat al-Baqarah: 187)

WHEN SHOULD ONE ENTER THE MASJID?

The formal timing of entering the Masjid is what Imaam Maalik, Anas and Sufyaan said, that you go at the Maghrib of the twentieth day and you leave at the Maghrib of the final day of Ramadhaan.

THE RULES OF I’TIKAAF

One must be a Muslim, it must be in a Masjid and you must have the intention of I’tikaaf. Women need the permission of their husband or Wali to do I’tikaaf, especially the permission of their husband (it is more essential). Just like she needs his permission to do the Sunnah of Siyaam, she needs his permission to do I’tikaaf because both are Sunnah.

I’TIKAAF FOR WOMEN

Many sisters say well we heard that there is no I’tikaaf for women. No, it is Sunnah for women to do I’tikaaf just like men. It is permissible for them, it is reward and if they can do it they should do it if there is no Fitnah. Some Masaajid, you hear about stuff that they do in I’tikaaf, I say it is Haraam for them to do I’tikaaf.
Allah said:
...وَأَنتُمْ عَاكِفُونَ فِي الْمَسَاجِدِ... ﴿البقرة: ١٨٧﴾
While you are in I’tikaaf (i.e. confining oneself in a mosque for prayers and invocations leaving the worldly activities) in the mosques. (Surat al-Baqarah: 187)
It is for men and woman as long as there is no Fitnah. In Sahih al-Bukhari, Aishah radhiallahu ‘anha said that the Prophet sallallahu ‘alayhi wa sallam allowed her and Hafsah to perform I’tikaaf.
There was one time that the Prophet sallallahu ‘alayhi wa sallam saw many tents in the Masjid. Note, they built tents for the women to stay in privacy and not to go mix and mingle. He ordered them to be taken down, he cancelled I’tikaaf himself and he made up for it the following month. Notice he ordered that they be taken down and he cancelled it himself. Why did he do that? There is a reason behind that. Some of the ‘Ulamaa said they were ordered to take them down because he disliked them to do I’tikaaf, because he may have sensed jealousy and competition. They wanted to be close to him, there is a jealousy factor and they are there near him, which defeats the purpose of I’tikaaf. The purpose of I’tikaaf is to get away from everything as much as possible and now they are near him, so it may have been a distraction. That is one opinion.
Other ‘Ulamaa said it was not to deter women from I’tikaaf, but rather because there were so many tents in the Masjid that there was not sufficient space for the men to do their obligatory matters. We have a clear, solid, authentic Hadith where the Prophet sallallahu ‘alayhi wa sallam permitted Aishah and Hafsah to do I’tikaaf and that is what stands.
In fact, more decisive and more direct than that is what is in Bukhari and Muslim:
أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَعْتَكِفُ فِي الْعَشْرَ الْأَوَاخِرَ مِنْ رَمَضَانَ حَتَّى تَوَفَّاهُ اللَّهُ ثُمَّ اعْتَكَفَ أَزْوَاجُهُ مِنْ بَعْدِهِ
The Hadith by ‘Urwah. This is after the Prophet sallallahu ‘alayhi wa sallam died and ‘Urwah says that the wives of the Prophet sallallahu ‘alayhi wa sallam did I’tikaaf after him. That is the overwhelming opinion of the great, vast majority of the ‘Ulamaa and of the Madhaahib, that a woman is like a man in I’tikaaf. Make sure you have permission and also that there is no Fitnah.

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Jazak Allah khair