he asked Ibn Umar about the length of the two Rak'ah (before) Al-Fajr. He said: "The Prophet would pray two and two during the night, and he would perform Al-Witr with one Rak'ah. And he would pray two Rak'ah while he was hearing the Adhan [meaning that they were light]."  

كَانَ النَّبِيُّ ﷺ يُصَلِّي مِنَ اللَّيْلِ مَثْنَى مَثْنَى وَيُوتِرُ بِرَكْعَةٍ وَكَانَ يُصَلِّي الرَّكْعَتَيْنِ وَالأَذَانُ فِي أُذُنِهِ يَعَنِي يُخَفِّفُ قَالَ وَفِي الْبَابِ عَنْ عَائِشَةَ وَجَابِرٍ وَالْفَضْلِ بْنِ عَبَّاسٍ وَأَبِي أَيُّوبَ وَابْنِ عَبَّاسٍ