Sunan Abu Dawud
1311
Sahih+3

Narrated Abu Hurairah:The Messenger of Allah (ﷺ) as saying: When one of you gets up by night (to pray), and falters in reciting the Qur'an (due to sleep), and he does not understand what he utters, he should sleep

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid