The Messenger of Allah (may Allah's peace and blessings be upon him) married her when he was outside the state of Ihrām
Authentic hadithعن يَزِيد بن الأصمِّ قال: حدَّثَتْني مَيْمونَة بنت الحارث رضي الله عنها «أن رسول الله صلى الله عليه وسلم تَزَوَّجها وهو حلال»، قال: «وكانت خالَتي، وخالةَ ابنِ عباس».
Yazīd ibn al-Asamm (may Allah have mercy upon him) reported: 'Maymūnah bint al-Hārith (may Allah be pleased with her) told me that the Messenger of Allah (may Allah's peace and blessings be upon him) married her when he was outside the state of Ihrām.' He added: ''She was my maternal aunt and the maternal aunt of Ibn ‘Abbās.’'
Explanation
Yazīd ibn al-Asamm says that the Mother of the Believers Maymūnah bint al-Hārith (may Allah be pleased with her) told him that the Messenger of Allah (may Allah's peace and blessings be upon him) married her when he was outside the state of Ihrām. When he married her, he was not assuming Ihrām for Hajj or ‘Umrah. Yazīd then mentioned his relation to Maymūnah (may Allah be pleased with her) as she was his maternal aunt, and the maternal aunt of Ibn ‘Abbās (may Allah be pleased with him) as well. This indicates his close relationship with Maymūnah, and proves that the Prophet (may Allah's peace and blessings be upon him) was not in the state of Ihrām as Ibn ‘Abbās said.
Source · Narrated by Muslim
From the Hadith Encyclopedia (hadeethenc.com).