Mishkat al-Masabih 19 Jihad كتاب الجهاد 241

وَعَنِ ابْنِ عُمَرَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَامَ يَعْنِي يَوْمَ بَدْرٍ فَقَالَ: «إِنَّ عُثْمَانَ انْطَلَقَ فِي حَاجَةِ اللَّهِ وَحَاجَةِ رَسُولِهِ وَإِنِّي أُبَايِعُ لَهُ» فَضَرَبَ لَهُ رسولُ الله بِسَهْمٍ وَلَمْ يَضْرِبْ بِشَيْءٍ لِأَحَدٍ غَابَ غَيْرَهُ. رَوَاهُ أَبُو دَاوُد

Ibn ‘Umar told that God’s Messenger stood up, i.e. on the day of Badr, and said, ‘Uthman has gone off on the business of God and His Messenger and I shall take the oath of allegiance on his behalf. God’s Messenger then appointed him a share, but did not do so for anyone else who was absent. Abu Dawud transmitted it.