Hazrat Aisha, may Allah be pleased with her, narrates, “The Holy Prophet, peace and blessings of Allah be upon him, sent (an army unit) under the command of a man who used to lead his companions in prayers and would finish his recitation with, ‘Say (O Muhammad), “He is Allah, the One.”’ [Surah al-Ikhlas, Ch.112 V.2]. When they returned (from the battle), they mentioned that to the Prophetsa. He said (to them), ‘Ask him why he does so.’ They asked him and he said, ‘I do so because it mentions the qualities of the Beneficent and I love to recite it (in my prayer).’ The Prophetsa said (to them), ‘Tell him that Allah loves him.’
(Sahih al-Bukhari, Kitab al-Tawhid)