Musnad Ahmad 288:22

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from an-Nu‘man ibn Salim, from Ibn Abi Aws, he said: My grandfather, Aws, would sometimes pray and gesture to me while he was in prayer, so I would give him his sandals. And he would say: "I saw the Messenger of Allah, may Allah bless him and grant him peace, praying in his sandals."