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. (Using translation from Abū Dāʾūd 1311)  

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا قَامَ أَحَدُكُمْ مِنَ اللَّيْلِ فَاسْتَعْجَمَ الْقُرْآنُ عَلَى لِسَانِهِ فَلَمْ يَدْرِ مَا يَقُولُ فَلْيَضْطَجِعْ