Yakshas were someone who used to sing in the heaven. That's what I think they are. So, these seven yakshas once go to the hut of Maharshi (great sage) Vashishtha. Maharshi Vashishtha was a very calm person. So calm that he forgave Maharshi Vishwamitra when Maharshi Vishwamitra killed his hundred sons. Well, we will meet both Maharshi Vishwamitra and Maharshi Vashishtha in the Ramayana.

The seven yakshas saw Nandini, daughter of Kaamdhenu. As I have told you earlier, kaamdhenu is this type of mythological cow which can produce as much food as she wants and Nandini had this same property.

Firstly, the seven yakshas were happy with the hospitality because they thought that his wife made all that food but then they saw the plates placed in front of Nandini and they would get filled by themselves. Suddenly, Maharshi Vashishtha had to go somewhere. So, he left and as soon as he left, one of the yakshas tried to kill Nandini because they already had kaamdhenu in the heaven and they were jealous that someone else has this kind of cow.

As soon as Maharshi Vashishtha felt that his cow was slaughtered, he came back and cursed them, "You all will be born in the mortal world (earth)." Now, deliberately slaughtering a cow is a big sin in Hinduism. That's why this matter was this serious.

They started pleading towards him and he sighed and said, "Okay, you will be killed and freed the moment you would be born but the one who killed Nandini will have to live on earth for much longer than humans can."

And guess who that Yaksha was? Of course Bhishma, who had the blessing of ichhamrityu, which would become a curse for him on his deathbed...