Is it permissible for the son of a man who was nursed by a woman to enter upon her during her period of mourning (iddah) after the death of her husband, knowing that the woman is the man's sister through fosterage?

There is no impediment for a man's son to enter upon his foster-sister, for she is his paternal aunt through fosterage (radāʿah) and one of his unmarriageable kin (maḥārim). Fosterage prohibits what lineage prohibits. It is permissible for him to enter upon her even if she is in her iddah (waiting period) due to the death of her husband. A woman in iddah is permitted to sit with her maḥārim, see them, and be seen by them. She is also permitted to speak with a non-mahram man when necessary, provided it adheres to শরীʿah guidelines.