It was narrated that Aishah said:
"The Messenger of Allah (ﷺ) said: 'If a man feels drowsy when he is praying, let him stop, lest he supplicate against himself without realizing.'" (ES)
English reference (ES): Vol. 1, Book 1, Hadith 162 (ES)
Arabic reference (ES): Book 1, Hadith 163 (ES)