Musnad Ahmad 1163:44

'Abd al-Samad narrated to us, he said: My father narrated to me, he said: Hanzalah narrated to us, he said: 'Abdullah ibn al-Harith ibn Nawfal narrated to us, he said: Mu'awiyah ibn Abi Sufyan led us in the afternoon prayer (Asr), then he sent [a messenger] to Maymunah, then he followed him with another man. She said: "The Messenger of Allah (peace and blessings of Allah be upon him) was preparing an expedition, and he did not have any mounts. Then some mounts from the charity (Sadaqah) came to him, and he began distributing them among them. They detained him until the time for Asr became late. He used to pray two rak'ahs before Asr, or whatever Allah willed. So he prayed [Asr], then he returned and prayed what he used to pray before it. And he, when he prayed a prayer or did a deed, liked to be constant in it."