Musnad Ahmad 1034:131

'Abd al-Rahman narrated to us, from Sufyan, from Abu Ishaq, some of our companions narrated to me, from Hudhayfah, that the polytheists took him and his father, and they took a pledge from them that they would not fight them on the day of Badr. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Fulfill [the pledge] to them, and we seek the help of Allah against them."