Bismillahir rahmanir rahim.
Alhamdulillah

Ibn Abi Nu’m se rivayat hai ki ek shaksh ne Abdullah bin umar radi allahu Anhuma se pucha ki agar koi shaksh (ehraam ki halat mein) makhkhi maar de to uska kaffara kya hoga is par Abdullah bin Umar Radi Allahu Anhu ne farmaya Iraq ke log makhkhi ke baarey mein sawal kartey hain jabki yahi log RasoollAllah Sallallahu Alaihi Wa sallam ke nawasey ko Qatl kar chukey hain jinkey baarey mein Nabi E Karim Sallallahu Alaihi Wa sallam ne farmaya tha ki ye dono (Hasan aur Hussain) Duniya mein mere Do khusbudar phool hain.
[Sahih Bukhari, 3753]

English:
Narrated Ibn Abi Nu’m radi allahu anhu : A person asked ‘Abdullah bin ‘Umar radi allahu anhu whether a Muslim could kill flies. I heard him saying (in reply). “The people of Iraq are asking about the killing of flies while they themselves murdered the son of the daughter of Allah’s Apostle . The Prophet Sallallahu Alaihi Wasallam said, They (i.e. Hasan and Husain RadiAllahu Anhum) are my two sweet basils in this world.”
[Sahih Bukhari, Book #57, Hadith #96]