Musnad Ahmad 32:1099

Hammad ibn Usamah narrated to us, from Sulayman ibn al-Mughirah, from Thabit, from Anas, who said: Abu Talhah came on the day of Hunayn, and the Messenger of Allah, may Allah bless him and grant him peace, was laughing at Umm Sulaym. He said: "O Messenger of Allah, have you not seen Umm Sulaym wearing a dagger?" The Messenger of Allah, may Allah bless him and grant him peace, said to her: "What are you doing with it, O Umm Sulaym?" She said: "I intended that if one of them drew near to me, I would stab him with it."