It is reported that Al-Ḥasan Al-Baṣrī – Allāh have mercy on him – said when asked ‘what is īmān (faith)?’:

It is perseverance (al-ṣabr) from the things that are forbidden by Allāh the Mighty and Majestic and acceptance. He was asked, “What is perseverance and acceptance?” He replied, “al-ṣabr is to persevere in holding back from what Allāh has forbidden, and [acceptance is] acceptance of what Allāh the Mighty and Majestic has commanded.”

Abū Bakr Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-‘Ilm 3:535.