The Angels were sent to destroy the People of the Prophet Lut

Allah the Exalted said about Ibrahim, peace be upon him,

فَلَمَّا ذَهَبَ عَنْ إِبْرَهِيمَ الرَّوْعُ وَجَآءَتْهُ الْبُشْرَى يُجَـدِلُنَا فِى قَوْمِ لُوطٍ - إِنَّ إِبْرَهِيمَ لَحَلِيمٌ أَوَّاهٌ مُّنِيبٌ - يإِبْرَهِيمُ أَعْرِضْ عَنْ هَـذَآ إِنَّهُ قَدْ جَآءَ أَمْرُ رَبِّكَ وَإِنَّهُمْ آتِيهِمْ عَذَابٌ غَيْرُ مَرْدُودٍ

When, in the course of the conversation, Holy Prophet Ibrahim (علیہ السلام) discovered that the guests were angels, he asked them what was their mission and they replied that they had been sent to the people of Lut (علیہ السلام) to destroy them as a punishment for their unspeakable crime. They would be stoned to death, but not with large stones.