Musnad Ahmad 949:10

Abu al-Nadr narrated to us, Hashraj ibn Nabatah al-Absi, a Kufan, narrated to us, Sa’id ibn Jumhan narrated to us, Safinah narrated to me, he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The Caliphate in my Ummah will be thirty years, then there will be kingship after that." Then Safinah said to me: "Hold the Caliphate of Abu Bakr, and the Caliphate of Umar, and the Caliphate of Uthman, and the Caliphate of Ali." He said: "So we found it to be thirty years. Then I looked after that at the Caliphs, and I did not find that thirty years applied to them." I said to Sa’id: "Where did you meet Safinah?" He said: "I met him at Batn Nakhla during the time of al-Hajjaj, and I stayed with him for eight nights asking him about the Hadiths of the Messenger of Allah, may Allah bless him and grant him peace." He said: I said to him: "What is your name?" He said: "I will not inform you; the Messenger of Allah, may Allah bless him and grant him peace, named me Safinah (Ship)." I said: "Why did he name you Safinah?" He said: "The Messenger of Allah, may Allah bless him and grant him peace, went out with his companions, and their luggage became heavy for them. He said to me: 'Spread your cloak.' So I spread it, and they placed their luggage in it, then they loaded it upon me. The Messenger of Allah, may Allah bless him and grant him peace, said to me: 'Carry it, for you are but a ship.' If I had carried on that day the load of a camel, or two, or three, or four, or five, or six, or seven, it would not have been heavy for me, except that it might have chafed."