Musnad Ahmad 1153:2049

Rawh narrated to us, Ibn Jurayj narrated to us, he said: Abdullah ibn Abi Mulaykah informed me, from a man from Banu Tamim whom we do not deem a liar, he said: Aisha was informed that Ibn Umar says: The Messenger of Allah (ﷺ) said: "The month is twenty-nine." Aisha denied that and said: May Allah forgive Abu Abd al-Rahman, the Messenger of Allah (ﷺ) did not say it like that, but he said: "The month may be twenty-nine."