Musannaf Ibn Abi Shayba 3:1329

Ubayd Allah ibn Musa narrated to us, from Uthman ibn al-Aswad, from Ikrimah ibn Khalid, who said: Abu Bakr ibn Abd al-Rahman ibn al-Harith ibn Hisham would not combine two surahs in one rak'ah. And he would not go beyond a surah when he finished it until he bowed.