Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) delivered a sermon in the year of the Conquest of Makkah, and he (peace and blessings be upon him) said: "O people! Whatever pact anyone had in the Jahiliyyah, Islam only makes it stronger; and there is no (wrong) pact in Islam. The Muslims are one body and one force against those besides them; the lowest of them may grant protection on their behalf, the farthest of them returns (the spoils) to them, and (the spoils of) their raiding parties are returned to those who stay behind." It is a portion of a long hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12929