Musnad Ahmad 1167:50

Yunus narrated to us, he said: 'Imran ibn Yazid narrated to us, from Mansur, from his mother, from Asma', she said: We went out with the Messenger of Allah, may Allah bless him and grant him peace, having entered into the state of Ihram for Hajj. She said: So he said to us: "Whoever has a sacrificial animal with him, let him remain in his state of Ihram, and whoever does not have a sacrificial animal with him, let him exit the state of Ihram."