Musnad Ahmad 1167:42

Ibn Numayr narrated to us, he said: Uthman ibn Hakim narrated to us, from Abu Bakr ibn Abdullah ibn al-Zubayr, from his grandmother—and I do not know if it is Asma bint Abi Bakr or Sa’da bint ‘Awf—that the Messenger of Allah, peace and blessings of Allah be upon him, entered upon Duba’a bint Abd al-Muttalib and said: "What prevents you from the Hajj, O aunt?" She said: "I am a sickly woman, and I fear being detained." He said: "Then enter into Ihram, and make the condition that your place of exiting Ihram is wherever you are detained."