Musannaf Ibn Abi Shayba 16:672

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Al-A’mash narrated to us, from Sulayman ibn Maysarah, from Tariq ibn Shihab, from Rafi’ ibn Abi Rafi’, who said: I saw Abu Bakr, and he had a Fadaki cloak. He would fasten it upon himself when he rode, and I and he would wear it when we dismounted. It was the cloak that the Hawazin taunted him about. They said: "So, the lawful has become permissible after the Messenger of Allah, may Allah bless him and grant him peace."