Narrated Ibn Abi Nu'm: `Abdullah bin `Umar was asked about a muhrim (a person in the state of pilgrimage). Shu'bah (a subnarrator) said "I think killing flies." I heard him saying (in reply). "The people of Iraq are asking about flies while they themselves murdered the son of the daughter of Allah's Messenger. The Prophet (ﷺ) said, 'They (i.e. Hasan and Husain) are my two sweet basils in this world.' "
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، عَنْ مُحَمَّدِ بْنِ أَبِي يَعْقُوبَ، سَمِعْتُ ابْنَ أَبِي نُعْمٍ، سَمِعْتُ عَبْدَ اللَّهِ بْنَ عُمَرَ، وَسَأَلَهُ، عَنِ الْمُحْرِمِ،، قَالَ شُعْبَةُ أَحْسِبُهُ يَقْتُلُ الذُّبَابَ فَقَالَ أَهْلُ الْعِرَاقِ يَسْأَلُونَ عَنِ الذُّبَابِ وَقَدْ قَتَلُوا ابْنَ ابْنَةِ رَسُولِ اللَّهِ صلى الله عليه وسلم، وَقَالَ النَّبِيُّ صلى الله عليه وسلم " هُمَا رَيْحَانَتَاىَ مِنَ الدُّنْيَا ".
sunnah.com