It is not surprising...
Do you not see that I give full measure, and (that) I am the best of hosts?’” Yusuf was very compassionate and kind towards his brothers. When he was speaking with them, they told him that they were ten brothers from a single father named Ya‘qub, the grandson of ’Ibrahim al Khalil, the great prophet of Allah. They told him that had he known their father, he would have had more respect for them, but their aged and venerable father was greatly saddened and depressed.
On asking them why their father had been so grief stricken, they replied that he had had a son whom he loved very much and who was the youngest of all his sons. This son had gone hunting and playing with them in the fields and when they had neglected him a wolf came upon him and killed him. Since then, their father had been weeping and grieving for him.
Some commentators have narrated that Yusuf was in the habit of not selling more than one camel load of grain per person, and as the brothers were ten, he sold them ten loads of grain. On receiving the grain, they said that their father, because of intensive grief, could not travel, as well as a younger brother who had stayed with him to serve him and keep his company, so they asked for a share for those two as well.
Yusuf ordered his men to add to their share, then turning towards them he told them to bring along the younger brother with them as a sign the next time they came back.