Is it permissible for a scholar to be blind? And is there a Hadith to that effect?

There is no harm in a scholar being blind, and there is no harm in benefiting from him during his blindness, whether he was sighted then became blind or was blind from birth. This is evidenced by its occurrence in Islamic history, as Ibn Umm Maktum, Ka'b ibn Malik, Waraqah ibn Nawfal, Ibn Abbas, and others among the scholars were blind, and people learned from them and benefited from their knowledge. Examples of this in the present era include Sheikh Ibn Baz and Sheikh Kishk.