It is narrated from Sayyiduna Salamah bin Salamah bin Waqsh (may Allah be pleased with him), and he was the last of the Companions; Sayyiduna Anas bin Malik (may Allah be pleased with him) was not the last, because he lived on after him. The two of them went to a wedding feast (walimah). Sayyiduna Salamah (may Allah be pleased with him) was in a state of ablution. They ate, then went out, and Sayyiduna Salamah (may Allah be pleased with him) performed ablution. Jubayrah said to him: Were you not in a state of ablution? He said: Yes indeed! But I saw the Messenger of Allah (peace and blessings be upon him) when we came out of a feast to which we had been invited, and the Messenger of Allah (peace and blessings be upon him) was in a state of ablution; he (peace and blessings be upon him) ate, then performed ablution. I said to him: O Messenger of Allah (peace and blessings be upon him)! Were you not in a state of ablution? He (peace and blessings be upon him) said: "Yes indeed, but new rulings keep coming, and this is a new ruling."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 726