It is narrated from Sa'id bin al-Musayyib (may Allah have mercy on him) that he said: "He is mistaken who stated that the Messenger of Allah (ﷺ) married Maymunah while in the state of ihram; the Messenger of Allah (ﷺ) married her while he was not in ihram."
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 877
Hadith Takhrijاسناده ضعيف لإرساله: اخرجه ابوداود، المناسك باب المحرم يتزوج ، رقم : 1845 ۔ والبيهقي: 212/7 ۔ وفي المعرفة السنن والآثار له (2890)۔