The Prophet ﷺ said: "Prayers at night are two by two, then if you fear that dawn will come, pray witr with one rak'ah." (Using translation from Nasāʾī 1668)
عَنِ النَّبِيِّ ﷺ قَالَ «صَلَاةُ اللَّيْلِ مَثْنَى مَثْنَى فَإِذَا خِفْتَ الصُّبْحَ فَأَوْتِرْ بِوَاحِدَةٍ»