Musnad Ahmad 329:42

'Affan narrated to us, he said: Wuhayb narrated to us, he said: 'Amr ibn Yahya narrated to us, from 'Abbad ibn Tamim, from 'Abdullah ibn Zayd, who said: When the time of al-Harrah came, someone came to him and said: "This is the son of Hanzalah." And 'Affan said once: "That is the son of Hanzalah, he is taking the pledge of allegiance from the people." He said: "Upon what is he taking their pledge?" He said: "Upon death." He said: "I will not pledge allegiance to anyone for this after the Messenger of Allah, may Allah bless him and grant him peace."