Musnad Ahmad 1156:188

Hajjaj narrated to us, Layth narrated to us, he said: ‘Uqayl narrated to us, from Ibn Shihab, that he said: Abu ‘Ubaydah ibn ‘Abd Allah ibn Zam‘ah informed me, that his mother, Zaynab bint Abi Salamah, informed him that her mother, Umm Salamah, the wife of the Prophet (may Allah bless him and grant him peace), used to say: The rest of the wives of the Prophet (may Allah bless him and grant him peace) refused to let anyone enter upon them through that breastfeeding. They said to ‘Aishah: "By Allah, we do not see this except as a concession that the Messenger of Allah (may Allah bless him and grant him peace) granted to Salim specifically. So, no one is entering upon us by this breastfeeding, nor are we seeing them."