A man asked the Messenger of Allah ﷺ about the prayer at night. The Messenger of Allah ﷺ 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. (Using translation from Abū Dāʾūd 1326)   

سَأَلَ رَجُلٌ رَسُولَ اللَّهِ ﷺ عَنْ صَلَاةِ اللَّيْلِ فَقَالَ «مَثْنَى مَثْنَى فَإِذَا خَشِيَ أَحَدُكُمُ الصُّبْحَ فَلْيُصَلِّ رَكْعَةً وَاحِدَةً تُوتِرُ مَا قَدْ صَلَّى»