Musannaf Ibn Abi Shayba 3:3892

Ibn Mahdi narrated to us, from Sulayman ibn Bilal, from Hisham ibn Urwah, who said: I saw Aban ibn Uthman combining the two prayers on a rainy night, the Maghrib and the Isha, and he prayed them together. Urwah ibn al-Zubayr, Sa’id ibn al-Musayyib, Abu Bakr ibn Abd al-Rahman, and Abu Salamah ibn Abd al-Rahman were with him, and they did not disapprove of it.