Musnad Ahmad 1302:35

'Affan narrated to us, Hammam narrated to us, he said: 'Asim ibn Bahdalah narrated to us, from Abu Salih, from Mu'adh ibn Jabal, that when he was dying, he said: "Bring the people to me." So they brought them to him. He said: "I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: 'Whoever dies not associating anything with Allah, Allah will place him in Paradise.' And I would not have told you this except at the time of death." And the witness to that is 'Uwaymir Abu al-Darda'. So they went to Abu al-Darda', and he said: "My brother spoke the truth, and he would not have told you what he told you except at the time of his death."