Musnad Ahmad 1156:118

Ya'qub narrated to us, he said: My father narrated to us, he said: Ibn Ishaq claimed, from Abu Bakr ibn Muhammad ibn 'Amr, from Abu Salamah, from Umm Salamah, she said: The Messenger of Allah, peace and blessings of Allah be upon him, came to Duba'ah bint az-Zubayr ibn 'Abd al-Muttalib while she was ailing. He said: "Will you not go out with us on this journey of ours?"—and he was intending the Farewell Pilgrimage. She said: "O Messenger of Allah, I am ailing, and I fear that my ailment will detain me." He said: "Then enter into the state of Ihram for Hajj, and say: 'O Allah, my place of exiting Ihram is wherever You detain me.'"