Musnad Ahmad 30:3433

Yazid narrated to us, Ibn Abi Dhi’b informed us, and Abu ‘Amir said: Ibn Abi Dhi’b narrated to us, from ‘Ajlan, the freed slave of al-Musham’il—and Abu ‘Amir said: the freed slave of Hakim, and Abu Ahmad al-Zubayri said: the freed slave of Hamas—from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace, who said: "Do not revile while you are fasting. If someone reviles you, then say: 'I am fasting.' And if you are standing, then sit down. By the One in whose hand is the soul of Muhammad, the change in the breath of the mouth of the fasting person is more pleasant to Allah than the scent of musk."