The Prophet ﷺ went out to open ground to answer a call of nature and did not find anyone to follow him. Umar went out and followed him with a clay pot or wudu vessel. He found him prostrating in a river bed. 

He fell back and sat behind him until the Prophet ﷺ lifted his head. He said: “You have done well, Umar. When you found me prostrating, you went behind me. Jibril came to me and said: If someone sends the salawat on you once, Allah will send blessings upon ten times on him and raise him ten degrees.”

أَنَّ النَّبِيَّ ﷺ خَرَجَ يَتَبَرَّزُ فَلَمْ يَجِدْ أَحَدًا يَتْبَعُهُ فَخَرَجَ عُمَرُ فَاتَّبَعَهُ بِفَخَّارَةٍ أَوْ مِطْهَرَةٍ فَوَجَدَهُ سَاجِدًا فِي مِسْرَبٍ فَتَنَحَّى 

فَجَلَسَ وَرَاءَهُ حَتَّى رَفَعَ النَّبِيُّ ﷺ رَأْسَهُ فَقَالَ: «أَحْسَنْتَ يَا عُمَرُ، حِينَ وَجَدْتَنِي سَاجِدًا فَتَنَحَّيْتَ عَنِّي، إِنَّ جِبْرِيلَ جَاءَنِي فَقَالَ: مَنْ صَلَّى عَلَيْكَ وَاحِدَةً صَلَّى اللَّهُ عَلَيْهِ عَشْرًا وَرَفَعَ لَهُ عَشْرَ دَرَجَاتٍ»