Homer sometimes nods

(even) Homer sometimes nods (Nobody, even a poet as great as the Greek epic writer Homer, can be at his best or most alert all the time.) -- и на старуху бывает проруха; и на солнце бывают пятна; на всякого мудреца довольно простоты

comes from Latin : 'Quandoque bonus dormitat Homerus' ...

Nods here means ‘becomes drowsy, falls asleep’; hence, ‘errs due to momentary lack of attention’. The source is {Horace Ars Poetica 359} indignor quandoque bonus dormitat Homerus, = I am indignant when worthy Homer nods.