775.1 - It was narrated from Anas ibn Malik (may Allah be pleased with him) that there was a man of the Ansar who used to lead them in prayer in the mosque of Quba’. Every time he led them and wanted to recite a surah, he would recite {QulHuwa Allahu ahad (Say, “He is Allah, [who is] One…)}  [al-Ikhlas] until he finished it, then he would recite another surah with it, and he would do that in every rak‘ah. His companions spoke to him about that, saying: You always start with this surah, then you think it is not enough, so you recite another surah. Either recite it only, or do not recite it and recite another surah instead. He said: I will not stop reciting it; if you want me to carry on leading you in prayer like this, I will do so, and if you do not like it, I will leave you. They thought that he was one of the best of them, and they did not want anyone else to lead them in prayer. So when the Prophet (blessings and peace of Allah be upon him) came to them, they told him about that, and he said: “O So-and-so, what prevented you from doing what your companions toldyou to do? What made you persist in reciting this surah in every rak‘ah?” He said: Because I love it. He said: “Your love for it has gained you admittance to Paradise.”.

Commentary : Surat al-Ikhlasis one of the greatest surahs in the Qur’an. Even though its words are few, it contains sublime and important meanings, as it clearly explains the concept of Tawhid (the oneness of Allah), the importance of worshipping Him alone and turning to Him alone, and it categorically states that He has no son and no father (may He be glorified and exalted).
In this hadith, Anas ibn Malik (may Allah be pleased with him) narrates that a man of the Ansar – whose name was Kulthum ibn Hidm (may Allah be pleased with him) – used to lead his companions in prayer in the mosque of Quba’, which was the first mosque that the Prophet (blessings and peace of Allah be upon him) built in Madinah when he arrived in the city as a migrant. It stands at the entrance to Madinah for one who is coming from the direction of Makkah. Every time he wanted to recite a surah after al-Fatihah, he would recite before it {QulHuwa Allahu ahad  (Say, “He is Allah, [who is] One…)}  [al-Ikhlas], then he would recite another surah. His companions spoke to him and told him that this surah on its own was sufficient for reciting after al-Fatihah, and by reciting it you will have done what is required of you in terms of recitation, so either recite it on its own, or recite the other surah that youwant to recite after it. But the man refused to do that, and gave them the choice between letting him continue to lead them in prayer in this manner, or appointing someone else to lead the prayer, if they did not like him to lead them. When the Prophet (blessings and peace of Allah be upon him) came to them, they told him about what this man was doing – the Prophet (blessings and peace of Allah be upon him) used to come to the mosque of Quba’ every Saturday to pray there, as it says in al-Sahihayn – so the Prophet (blessings and peace of Allah be upon him) asked him about the reason why he did not agree to what his companions were asking of him, and why he persisted in reciting {QulHuwa Allahu ahad  (Say, “He is Allah , [who is] One…)}  [al-Ikhlas] with every other surah he recited. The man told the Messenger of Allah (blessings and peace of Allah be upon him) that his love for Surat al-Ikhlas was what made him do that. The Prophet (blessings and peace of Allah be upon him) approved of him doing that, and gave him the glad tidings that his love for this surah had gained him admittance to Paradise. It is well-known that admittance to Paradise will only happen in the hereafter, but as it is inevitably going to happen, it is as if it has already happened, so the Prophet (blessings and peace of Allah be upon him) spoke in the past tense when he gave him this good news.
This hadith highlights the virtue of Surat al-Ikhlas.
It also indicates that it is permissible to recite two surahs [besides al-Fatihah] in one rak‘ah..