Mus'ab bin Sa'd narrates: Before Badr, the polytheists seized Sayyiduna Hudhayfah and his father and wanted to kill them. They took a covenant and pledge from them that they would not help against us, and then they released them both. The two of them came to the Prophet (peace and blessings be upon him) and said: "We have pledged to them that we will not help against them; but if you wish, we will fight alongside you." The Messenger of Allah (peace and blessings be upon him) said: "No, rather we will fulfil our pledge to them, and we will seek Allah's help against them."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2988