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."
Sunan an-Nasa'i Book 11, Hadith 118
← Previous Hadith "I watched the Messenger of Allah (ﷺ)- twenty times- reciting in the two rak'ahs after maghrib 'Say: O you disbelievers' and 'Say: He is Allah, (the) One.'"

Sunan an-Nasa'i Book 11, Hadith 117 Next Hadith → "I heard Abu Hurairah say: 'I came back (from a journey) with the Messenger of Allah (ﷺ) and he heard a man reciting 'Say: He is Allah, (the) One, Allah-us-Samad (the Self-Sufficient Master). He begets not, nor was He begotten. And there is none equal or comparable unto Him.' The Messenger of Allah (ﷺ) said: 'It is guaranteed.' We asked him: 'What, O Messenger of Allah?' He said: 'Paradise.'"

Sunan an-Nasa'i Book 11, Hadith 119