Aishah, may Allah (SWT) be pleased with her, told him that the Messenger of Allah ﷺ said: "There is no man who habitually prays at night, then sleep overwhelms him, but Allah (SWT) will record for him the reward of his prayer, and his sleep is a charity given to him." (Using translation from Nasāʾī 1784)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ «مَا مِنَ امْرِئٍ تَكُونُ لَهُ صَلَاةٌ بِلَيْلٍ فَغَلَبَهُ عَلَيْهَا نَوْمٌ إِلَّا كُتِبَ لَهُ أَجْرُ صَلَاتِهِ وَكَانَ نَوْمُهُ صَدَقَةً عَلَيْهِ»