Musnad Abu Ya'la al-Mawsili 1:9

Masruq ibn al-Marzuban al-Kufi narrated to us, he said: Abd al-Salam informed us, from Abdullah ibn Bishr, from al-Zuhri, from Sa'id ibn al-Musayyib, from Uthman ibn Affan, who said: When the Prophet, may Allah bless him and grant him peace, was taken [in death], some of his companions were overcome with distress, and I was among those who were distressed. He said: Then Umar passed by me and greeted me, but I did not return the greeting to him. So he complained about me to Abu Bakr. He said: So he [Abu Bakr] came to us and said to me: Your brother greeted you, but you did not return the greeting to him. I said: I did not know of his greeting, for I was preoccupied with that [matter]. He said: And why? I said: The Messenger of Allah, may Allah bless him and grant him peace, has been taken, and I did not ask him about the salvation of this matter. He said: But I did ask him. He said: So I stood up to him and embraced him. I said: May my father and mother be sacrificed for you, you are more entitled to that. He said: I asked him, and he said: "Whoever accepts the word which I offered to my uncle, it is salvation for him."