Musannaf Ibn Abi Shayba 27:552

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