عَنْ أَنَسِ بْنِ مَالِكٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: ((إِذَا نَعَسَ أَحَدُكُمْ وَهُوَ يُصَلِّي فَلْيَنْصَرِفْ فَلْيَنَمْ حَتَّى يَعْلَمَ مَا يَقُولُ))
Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: When any one of you becomes drowsy during prayer, he should leave the prayer and go to sleep until he understands what he is saying.