Musnad Abu Ya'la al-Mawsili 154:109

Zuhayr narrated to us, Abd al-Rahman narrated to us, Mahdi ibn Maymun narrated to us, from Muhammad ibn Abd Allah ibn Abi Ya'qub, from Ibn Abi Nu'm, that a man asked Ibn Umar about the blood of a mosquito. He said, "From where are you?" He said, "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, while I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'They are my two sweet basils from the world.'"