´Ibn Umar narrated that:` The Prophet (S) said: "Salat in the night is two by two. So when you fear the dawn (is near) then make it odd by one, and make that the last of your Salat odd."
Hadith Referenceسنن ترمذي / أبواب السهو / 437
Hadith Gradingالألبانی:صحيح، ابن ماجة (1319 و 1320)