The Messenger of Allah ﷺ sent a man on a campaign, and he used to recite to his companions when leading them in prayer, and would conclude with 'Say: He is Allah, (the) One.' When they returned, they told the Messenger of Allah ﷺ about that. He said: "Ask them why he did that." So they asked him and he said: "Because it is a description of the Most Merciful, the Mighty and Sublime, and I love to recite it." The Messenger of Allah ﷺ said: "Tell him that Allah (SWT), the Mighty and Sublime, loves him." (Using translation from Nasāʾī 993)
أَنَّ رَسُولَ اللهِ ﷺ بَعَثَ رَجُلًا عَلَى سَرِيَّةٍ وَكَانَ يَقْرَأُ لِأَصْحَابِهِ فِي صَلَاتِهِمْ فَيَخْتِمُ بِقُلْ هُوَ اللهُ أَحَدٌ فَلَمَّا رَجَعُوا ذَكَرُوا ذَلِكَ لِرَسُولِ اللهِ ﷺ فَقَالَ «سَلُوهُ لِأَيِّ شَيْءٍ صَنَعَ ذَلِكَ؟» فَسَأَلُوهُ فَقَالَ «لِأَنَّهَا صِفَةُ الرَّحْمَنِ فَأَنَا أَحَبُّ أَنْ أَقْرَأَ بِهَا» قَالَ رَسُولُ اللهِ ﷺ «أَخْبِرُوهُ أَنَّ اللهَ يُحِبُّهُ»