If a person is greeted while urinating

Isḥāq > Muʿādh b. Hishām from my father > Qatādah > al-Ḥasan > al-Ḥuḍayn > al-Muhājir b. Qunfudh

It was narrated from Al-Muhajir bin Qunfudh that he greeted the Prophet ﷺ with Salam while he was urinating, and he did not return the greeting until he had performed Wudu'. When he had performed Wudu' he returned the greeting. – Sound Chain

أَخْبَرَنَا إِسْحَاقُ حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ حَدَّثَنِي أَبِي عَنْ قَتَادَةَ عَنْ الْحَسَنِ عَنْ الْحُضَيْنِ عَنْ الْمُهَاجِرِ بْنِ قُنْفُذٍ

أَنَّهُ «سَلَّمَ عَلَى النَّبِيِّ ﷺ وَهُوَ يَبُولُ فَلَمْ يَرُدَّ عَلَيْهِ السَّلَامَ حَتَّى تَوَضَّأَ فَلَمَّا تَوَضَّأَ رَدَّهُ عَلَيْهِ» – إسناده صحيح