A person asked ʿAbdullah bin ʿUmar 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 Messenger of Allah ﷺ . The Prophet ﷺ said, They (i.e. Hasan and Husain) are my two sweet basils in this world." (Using translation from Bukhārī 3753)
عَنِ الذُّبَابِ وَقَدْ قَتَلُوا ابْنَ بِنْتِرَسُولِ اللهِ ﷺ وَقَدْ قَالَ رَسُولُ اللهِ ﷺ هُمَا رَيْحَانَتِي مِنَ الدُّنْيَا