Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: That I should swear nine times that the Messenger of Allah was killed is dearer to me than that I should swear once that he was not killed; that is because Allah Almighty made him a Prophet and also raised him to the rank of a martyr. Al-A'mash says: I mentioned this to Ibrahim al-Nakha'i, and he said: People used to hold that the Jews had poisoned the Prophet (peace and blessings be upon him) and Sayyiduna Abu Bakr (may Allah be pleased with him).
Ahmad recorded it, and its narrators are the narrators of the "Sahih".