Is it permissible for a divorced woman to observe her 'iddah in the house of a man who is a stranger to her, merely because he is blind?

Fatimah bint Qais observing her 'iddah in the house of Ibn Umm Maktum was out of necessity, because her husband had divorced her thrice, and she feared he might intrude upon her. The Prophet, peace and blessings be upon him, initially advised her to observe her 'iddah with Umm Sharik, then he commanded her to observe it with Ibn Umm Maktum because he was blind, so that she could lay aside her garments and feel safe.

Fatimah bint Qais observing her 'iddah with Ibn Umm Maktum does not imply permission for her to look at him. Rather, it was for her safety from the gaze of others, while she was still commanded to lower her gaze. This was the lesser of two harms.