The Prophet ﷺ said: Any person who offers prayer at night regularly but (on a certain night) he is dominated by sleep will be given the reward of praying. His sleep will be almsgiving.  

أَنَّ عَائِشَةَ زَوْجَ النَّبِيِّ ﷺ أَخْبَرَتْهُ أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَا مِنِ امْرِئٍ تَكُونُ لَهُ صَلاَةٌ بِلَيْلٍ يَغْلِبُهُ عَلَيْهَا نَوْمٌ إِلاَّ كُتِبَ لَهُ أَجْرُ صَلاَتِهِ وَكَانَ نَوْمُهُ عَلَيْهِ صَدَقَةً