The Prophet ﷺ sent a man to lead a military expedition, and this man used to lead his companions in prayer, always concluding his recitation with "Say, He is Allah, the One" [Ikhlas 112:1]. When they returned, they mentioned this to the Prophet ﷺ.He said, "Ask him why he does that."So they asked him, and he replied, "Because it describes the Most Merciful, and I love to recite it."The Prophet ﷺ said, "Tell him that Allah loves him."
أن النبي ﷺ بعث رجلا على سرية، وكان يقرأ لأصحابه في صلاته فيختم: ب{قل هو الله أحد}. فلما رجعوا ذكروا ذلك للنبي ﷺ فقال: سلوه لأي شيء يصنع ذلك؟ فسألوه فقال: لأنها صفة الرحمن، وأنا أحب أن أقرأ بها، فقال النبي ﷺ: أخبروه أن الله يحبه.
Bukhari narrated it in the Book of Monotheism (7375), and Muslim narrated it in the Book of the Prayer of Travelers (813), both through the route of Abdullah bin Wahb, who said, Amr bin Harith told us, from Saeed bin Abu Hilal, that Abu Rijal Muhammad bin Abdul-Rahman told him, from his mother Amra bint Abdul-Rahman, who had been raised under the care of Ayesha, the wife of the Prophetﷺ, from Ayesha, and then he related the hadith.