I went in to see Ayesha, and she said, "The Messenger of Allah ﷺ never performed Umrah except in Dhul-Qadah, and he performed Umrah three times."
حدثنا محمد بن سلمة عن أبي إسحاق عن يحيى بن عباد
دخلت على عائشة فقالت ما اعتمر رسول الله ﷺ إلا في ذي القعدة ولقد اعتمر ثلاث عمر
Its isnad is sahih, it was mentioned earlier in the dialogue between Ayesha and Ibn Umar. The hadith is found in Bukhari 3/600 no. 1780 (Fath al-Bari), Muslim 2/916 no. 253, and Abu Dawud 2/206 no. 1994.