Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: It was said to the Prophet (peace and blessings be upon him) after he had finished with Badr: "Go after the caravan; there is nothing standing in its way." Thereupon Abbas (may Allah be pleased with him), who was at that time bound in his captivity, said: "That is not right." The Messenger of Allah (peace and blessings be upon him) said: "Why?" He said: "Because Allah promised you one of the two parties, and Allah has granted you what He promised you."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11683