Sahih Bukhari Volume 4, Book 52, Hadith Number 138.

Narated By Anas : I was in the company of Jabir bin ‘Abdullah on a journey and he used to serve me though he was older than I. Jarir said, “I saw the Ansar doing a thing (i.e. showing great reverence to the Prophet) for which I have vowed that whenever I meet any of them, I will serve him.”