Musnad Ahmad 1007:3

Bishr ibn al-Mufaddal Abu Isma'il narrated to us, Abd al-Rahman—meaning Ibn Ishaq—narrated to us, from Zayd ibn Abi 'Attab, from 'Amr ibn Sulaym, from Abu Qatadah, who said: I saw the Messenger of Allah (may Allah bless him and grant him peace) while he was praying, carrying Umamah—or Umaymah—the daughter of Abu al-'As, and she was the daughter of Zaynab. He would carry her when he stood, and he would put her down when he bowed, until he finished.