Musnad Ahmad 25:517

Ya'qub narrated to us, Ibn Akhi Ibn Shihab narrated to us, from his uncle, 'Urwah ibn al-Zubayr narrated to me, that al-Miswar ibn Makhramah and 'Abd al-Rahman ibn 'Abd al-Qari narrated to him that they heard 'Umar ibn al-Khattab saying: I heard Hisham ibn Hakim ibn Hizam reciting—then he mentioned the hadith. Muhammad said: And 'Ubayd Allah ibn 'Abd Allah ibn 'Utbah ibn Mas'ud narrated to me, that Ibn 'Abbas narrated to him, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Gabriel recited to me upon one mode, so I requested him to increase it, and I did not cease asking him to increase it, and he increased it for me, until it reached seven modes."