That the Messenger of Allah ﷺ said that Jibra'il had indeed descended upon him to say to him: "Tell them - meaning your Companions - to choose regarding the captives of Badr, between either killing them or ransoming the, so that the amount killed by them will correspond similarly to them." So they said: "Ranson, even though some of us may be killed." There are narrations on this topic from Ibn Mas'ud, Anas, Abu Barzah, and Jubair bin Mut'im.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ جِبْرَائِيلَ هَبَطَ عَلَيْهِ فَقَالَ لَهُ خَيِّرْهُمْ يَعْنِي أَصْحَابَكَ فِي أُسَارَى بَدْرٍ الْقَتْلَ أَوِ الْفِدَاءَ عَلَى أَنْ يُقْتَلَ مِنْهُمْ قَابِلاً مِثْلُهُمْ قَالُوا الْفِدَاءَ وَيُقْتَلَ مِنَّا قَالَ وَفِي الْبَابِ عَنِ ابْنِ مَسْعُودٍ وَأَنَسٍ وَأَبِي بَرْزَةَ وَجُبَيْرِ بْنِ مُطْعِمٍ  

That the Prophet ﷺ ransomed two men for the Muslims with a man from the idolaters.  

أَنَّ النَّبِيَّ ﷺ فَدَى رَجُلَيْنِ مِنَ الْمُسْلِمِينَ بِرَجُلٍ مِنَ الْمُشْرِكِينَ