Musannaf Ibn Abi Shayba 3:3111

Ibn Fudayl narrated to us, from al-A’mash, from Muslim, who said: I used to sit with Masruq and Abu Ubaydah during the time of Ziyad. When the time for prayer would enter, they would stand and pray, then they would sit until the mu'adhdhin gave the adhan and the Imam came out; then they would stand and pray with him. And they would do the same for the Asr prayer.