Reciting Surah al-Ikhlas in salat

عَنْ عَائِشَةَ أَنَّ النَّبِيَّ صلى الله عليه وسلم بَعَثَ رَجُلاً عَلَى سَرِيَّةٍ، وَكَانَ يَقْرَأُ لأَصْحَابِهِ فِي صَلاَتِهِ فَيَخْتِمُ بِ ـ ‏{‏قُلْ هُوَ اللَّهُ أَحَدٌ‏}‏ فَلَمَّا رَجَعُوا ذَكَرُوا ذَلِكَ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ: سَلُوهُ لأَىِّ شَىْءٍ يَصْنَعُ ذَلِكَ‏‏.‏ فَسَأَلُوهُ فَقَالَ لأَنَّهَا صِفَةُ الرَّحْمَنِ، وَأَنَا أُحِبُّ أَنْ أَقْرَأَ بِهَا‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم: أَخْبِرُوهُ أَنَّ اللَّهَ يُحِبُّهُ‏‏.‏

Hazrat Aisha^ra narrated:“The Prophet^sa dispatched a man as commander of a detachment. In the prayers he led for his companions, he would conclude his recitation with ‘Qul Huwallahu Ahad…’ [i.e., Surah al-Ikhlas] When they returned, they mentioned this to the Prophet^sa. He said, ‘Ask him why he does that.’ They asked him, and he replied, ‘Because it describes the Most Merciful, and I love to recite it.’ The Prophet^sa said, ‘Tell him that Allah loves him.’”

(Sahih al-Bukhari, Kitab at-tawhid, Bab ma ja’a fi du‘a’i n-nabiyyi^sa ummatahu ila tawhidillahi tabaraka wa ta‘ala, Hadith 7375)