A man passed by the Prophet (sal Allaahu alayhi wa sallam ) while he was urinating, and saluted him. The Prophet (sal Allaahu alayhi wa sallam) did not return the salutation to him. Abu Dawud said : It is narrated on the authority of Ibn 'Umar that the Prophet (sal Allaahu alayhi wa sallam) performed tayammum, then he returned the salutation to the man.  

مَرَّ رَجُلٌ عَلَى النَّبِيِّ ﷺ وَهُوَ يَبُولُ فَسَلَّمَ عَلَيْهِ فَلَمْ يَرُدَّ عَلَيْهِ  

Muhajir came to the Prophet ﷺ while he was urinating. He saluted him. The Prophet ﷺ did not return the salutation to him until he performed ablution. He then apologised to him, saying: I disliked remembering Allah except in the state of purification.  

أَنَّهُ أَتَى النَّبِيَّ ﷺ وَهُوَ يَبُولُ فَسَلَّمَ عَلَيْهِ فَلَمْ يَرُدَّ عَلَيْهِ حَتَّى تَوَضَّأَ ثُمَّ اعْتَذَرَ إِلَيْهِ فَقَالَ إِنِّي كَرِهْتُ أَنْ أَذْكُرَ اللَّهَ ﷻ إِلاَّ عَلَى طُهْرٍ أَوْ قَالَ عَلَى طَهَارَةٍ