Musnad Ahmad 30:3835

Muhammad ibn Mus'ab narrated to us, al-Awza'i narrated to us, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurayrah, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "The right of the Muslim upon the Muslim is five: he greets him with peace when he meets him, he says 'Yarhamuk Allah' (may Allah have mercy on you) to him when he sneezes, he visits him when he is ill, he attends his funeral when he dies, and he answers him when he invites him." My father said: This is *gharib* (a rare narration), meaning this hadith.