Sayyiduna al-Agharr al-Muzani (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) assigned some dates for me from a man of the Ansar, but he kept putting me off, so I spoke to the Messenger of Allah (peace and blessings be upon him) about it. He (peace and blessings be upon him) said: "O Abu Bakr, go with him tomorrow morning and get him his dates." Sayyiduna Abu Bakr (may Allah be pleased with him) promised to meet me at the mosque after we had prayed Fajr. I found him where he had promised me, and we set off. Whenever a man saw Sayyiduna Abu Bakr from afar, he greeted him with salam. So Sayyiduna Abu Bakr (may Allah be pleased with him) said: "Do you not see how much virtue the people gain over you by getting ahead of you? Let no one precede you in giving salam." So whenever a man appeared, we would hasten to greet him with salam before he could greet us.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 876