Ibn Abi Nu'm narrates: I was with Sayyiduna Ibn Umar (may Allah be pleased with them both) when a man asked him about the blood of a mosquito. He said: Where are you from? He said: From the people of Iraq. He said: Look at this man! He is asking me about the blood of a mosquito, while they killed the grandson of the Messenger of Allah (peace and blessings be upon him)! And I heard the Messenger of Allah (peace and blessings be upon him) say: "These two (Hasan and Husayn) are my two sweet basils of this world."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2871