Abu Dawud
Prayer
Book Number: 002 / Hadith Number: 1321
Narated By 'Abd Allah b. 'Umar : A man asked the Apostle of Allah (pbuh) about the prayer at night. The Apostle of Allah (pbuh) said: Prayer during the night should consist of pairs of rak'ahs, but if one of you fears the morning is near he should pray one rak'ah which will make his prayer an odd number for him.