Musannaf Ibn Abi Shayba 28:1081

Muhammad ibn Fudayl narrated to us, from al-Walid ibn Jumay', from Habib ibn Abi Thabit, that Abu Bakr said to Khalid ibn al-Walid: "Bring me your spear." Then he tied a banner for him and said to him: "Proceed, for indeed Allah is with you."