Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) said: "Some matter arose among the Ansar, so the Messenger of Allah (peace and blessings be upon him) went to them to make peace between them. Then he came back, and the prayer had already begun, and Sayyiduna Abu Bakr (may Allah be pleased with him) was leading the people in prayer, so the Messenger of Allah (peace and blessings be upon him) prayed behind Sayyiduna Abu Bakr (may Allah be pleased with him)."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5795