Sayyiduna Hudhayfah bin al-Yaman (may Allah be pleased with him) narrates: The polytheists seized me and my father on the day of Badr and took a pledge from us that we would not help the Prophet (peace and blessings be upon him). We mentioned this to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Fulfil your pledge to them, and we will seek Allah's help against them."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2999