Imam Malik's Muwatta, Chapter: Jihad

Yahya related to me from Malik that Yahya ibn Said said, "On the Day of Uhud, The Messenger of Allah, may Allah bless him and grant him peace, said, 'Who will bring me news of Sad ibn al-Rabi al-Ansari?' a man said, 'Me, Messenger of Allah!' So the man went around among the slain, and Sad ibn al-Rabi said to him, 'What are you doing?' The man said to him, 'The Messenger of Allah, may Allah bless him and grant him peace, sent me to bring him news of you.' He said, 'Go to him, and give him my greetings, and tell him that I have been stabbed twelve times, and am mortally wounded. Tell your people that they will have no excuse with Allah if the Messenger of Allah, may Allah bless him and grant him peace, is slain while one of them is still alive.' "