Musannaf Ibn Abi Shayba 3:2799

Ibn Numayr narrated to us, he said: Sufyan narrated to us, from Tawbah, from al-Sha'bi, who said: When Shurayh would come to the Friday [prayer], if the Imam had not yet come out, he would pray two rak'ahs. And if he had come out, he would sit and clasp his knees with his hands, and face the Imam, and he would not turn to the right nor to the left.