Sunan Abi Dawud, Hadith 1987

Mujahid said: Ibn 'Umar was asked: How many times did the Messenger of Allah perform 'Umrah ? He said: Twice. 'Aishah said: Ibn 'Umar knew that the Messenger of Allah performed three 'Umrahs in addition to the one he combined with the Farewell Pilgrimage.

حَدَّثَنَا النُّفَيْلِيُّ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا أَبُو إِسْحَاقَ، عَنْ مُجَاهِدٍ، قَالَ سُئِلَ ابْنُ عُمَرَ كَمِ اعْتَمَرَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقَالَ مَرَّتَيْنِ ‏.‏ فَقَالَتْ عَائِشَةُ لَقَدْ عَلِمَ ابْنُ عُمَرَ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَدِ اعْتَمَرَ ثَلاَثًا سِوَى الَّتِي قَرَنَهَا بِحَجَّةِ الْوَدَاعِ ‏.‏

sunnah.com

also referenced under: Hadith 1992 (DarusSalam)