Musnad Ahmad 27:1481

Surayj narrated to us, Mahdi narrated to us, from Muhammad ibn Abi Ya’qub, from Ibn Abi Nu’m, who said: I was sitting with Ibn Umar when a man came to him asking about the blood of a mosquito. Ibn Umar said to him: "From whom are you?" He said: "I am from the people of Iraq." He said: "Look at this one, he asks me about the blood of a mosquito, and they have killed the son of the Messenger of Allah, may Allah bless him and grant him peace, while I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'They are both my two sweet basils from the world.'"