Musnad Ahmad 288:2

Yahya ibn Sa'id narrated to us, from Shu'bah, from al-Nu'man ibn Salim, from Ibn Abi Aws, from his grandfather, that his sandals would be brought to him while he was praying, so he would put them on. And he would say: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, praying in his sandals."