Anas bin Malik reported,
A man from the Ansar used to lead the people in prayer at the mosque of Quba. Whenever he began a surah to recite for them in the prayer, he would start with "Say, He is Allah, One" [Ikhlas 112:1] until he completed it, then he would recite another surah along with it. He did this in every rakah.His companions spoke to him about it and said, "You recite this surah, then you do not consider it sufficient until you recite another surah with it. Either recite it alone, or leave it and recite another surah."He replied, "I will not abandon it. If you wish for me to lead you in prayer with it, I will do so, and if you dislike that, I will leave you."They considered him the best among them and disliked the idea of anyone else leading them in prayer. When the Prophet came to them, they informed him of the matter.He said, "So-and-so, what prevents you from doing what your companions ask, and what makes you recite this surah in every rakah?"He answered, "Messenger of Allah, I love it."The Messenger of Allah ﷺ said, "Your love for it has admitted you into Paradise."
Azami 247
Sahihعن أنس بن مالك قال
كان رجل من الأنصار يؤمهم في مسجد قباء. فكان كلما افتتح سورة يقرأ لهم في الصلاة فقرأ بها، افتتح ب {قل هو الله أحد} حتى يفرغ منها، ثم يقرأ بسورة أخرى معها، وكان يصنع ذلك في كل ركعة. فكلمه أصحابه فقالوا: إنك تقرأ بهذه السورة، ثم لا ترى أنها تجزيك حتى تقرأ بسورة أخرى، فإما أن تقرأ بها، وإما أن تدعها وتقرأ بسورة أخرى، قال: ما أنا بتاركها، إن أحببتم أن أؤمكم بها فعلت وإن كرهتم تركتكم. وكانوا يرونه أفضلهم، وكرهوا أن يؤمهم غيره، فلما أتاهم النبي أخبروه الخبر. فقال: يا فلان ما يمنعك مما يأمر به أصحابك، وما يحملك أن تقرأ هذه السورة في كل ركعة؟ فقال: يا رسول الله إني أحبها، فقال رسول الله ﷺ: إن حبها أدخلك الجنة.
Tirmidhi (2901) reported it, saying, Muhammad bin Ismail (Bukhari) told us, Ismail bin Abu Uways told us, Abdul-Aziz bin Muhammad told us, from Ubaydullah bin Umar, from Thabit Bunani, from Anas bin Malik, and he related the hadith. Tirmidhi said, "It is hasan gharib sahih from this angle, from the hadith of Ubaydullah bin Umar, from Thabit. Mubarak bin Fadala also related it from Thabit, from Anas, that a man said, 'O Messenger of Allah, I love this surah, "Say, He is Allah, One", so he said, "Your love for it will admit you into Paradise."'" He said, Abu Dawud Sulayman bin Ashath told us this, Abu Walid told us, Mubarak bin Fadala told us this. End of quote.Bukhari mentioned it in the Book of Adhan (774) as a suspended report from Ubaydullah bin Umar, from Thabit, from Anas. I say, this is the very chain that Tirmidhi connected from Bukhari, from Ismail bin Abu Uways, as mentioned before.The Hafiz (Ibn Hajar) related in Fath al-Bari that Daraqutni said in his Ilal that Hammad bin Salama differed from Ubaydullah in its chain, relating it from Thabit, from Habib bin Subaya, as a mursal report, and he said this is closer to being correct. The Hafiz said, he gave it preference only because Hammad bin Salama has priority in matters relating to Thabit's hadiths. However, Ubaydullah bin Umar is a reliable master of hadith and an authority, and Mubarak agreed with him in his chain, so it is possible that Thabit had two teachers for this hadith. End of quote.I say, it is as he said. It is also well known that when a chain is disputed between being connected (marfu) and being disconnected (mursal), and the one who connects it is trustworthy, his addition is accepted by the majority of scholars. Ibn Khuzayma also graded it sahih and reported it in his Sahih (537), as did Ibn Hibban in his Sahih (794), both by the route of Abdul-Aziz bin Muhammad (Darawardi) with the same wording.As for the hadith of Mubarak bin Fadala, Tirmidhi reported it as mentioned before, and Darimi also reported it (3436), and Ibn Hibban graded it sahih (792), both of them by the route of Mubarak bin Fadala, in a shortened form. Mubarak bin Fadala is a mudallis narrator, but he explicitly stated that he was directly transmitting (tahdith) in Darimi's version.