Imam Ahmad recorded from Ubayy bin Ka`b that the idolators said to the Prophet , “O Muhammad! Tell us the lineage of your Lord.” So Allah revealed
﴿قُلْ هُوَ اللَّهُ أَحَدٌ – اللَّهُ الصَّمَدُ – لَمْ يَلِدْ وَلَمْ يُولَدْ – وَلَمْ يَكُنْ لَّهُ كُفُواً أَحَدٌ ﴾
(Say: “He is Allah, One. Allah He begets not, nor was He begotten. And there is non comparable to Him.”) Similar was recorded by At-Tirmidhi and Ibn Jarir and they added in their narration that he said,
“(As-Samad) is One Who does not give birth, nor was He born, because there is nothing that is born except that it will die, and there is nothing that dies except that it leaves behind inheritance, and indeed Allah does not die and He does not leave behind any inheritance.
﴿وَلَمْ يَكُنْ لَّهُ كُفُواً أَحَدٌ ﴾
(And there is none comparable to Him.) This means that there is none similar to Him, none equal to Him and there is nothing at all like Him.” Ibn Abi Hatim also recorded it and At-Tirmidhi mentioned it as a Mursal narration. Then At-Tirmidhi said, “And this is the most correct.”
Al-Bukhari reported from `Amrah bint `Abdur-Rahman, who used to stay in the apartment of `A’ishah, the wife of the Prophet , that `A’ishah said, “The Prophet sent a man as the commander of a war expedition and he used to lead his companions in prayer with recitation (of the Qur’an). And he would complete his recitation with the recitation of `Say: He is Allah, One.’ So when they returned they mentioned that to the Prophet and he said,
«سَلُوهُ لِأَيِّ شَيْءٍ يَصْنَعُ ذَلِكَ؟»
(Ask him why does he do that.) So they asked him and he said, `Because it is the description of Ar-Rahman and I love to recite it. So the Prophet said,
«أَخْبِرُوهُ أَنَّ اللهَ تَعَالَى يُحِبُّه»
(Inform him that Allah the Most High loves him.)” This is how Al-Bukhari recorded this Hadith in his Book of Tawhid. Muslim and An-Nasa’i also recorded it.
In his Book of Salah, Al-Bukhari recorded that Anas said, “A man from the Ansar used to lead the people in prayer in the Masjid of Quba’. Whenever he began a Surah in the recitation of the prayer that he was leading them, he would start by reciting `Say: He is Allah, One’ until he completed the entire Surah. Then he would recite another Surah along with it (after it). And used to do this in every Rak`ah. So his companions spoke to him about this saying; `Verily, you begin the prayer with this Surah. Then you think that it is not sufficient for you unless you recite another Surah as well. So you should either recite it or leave it and recite another Surah instead.’ The man replied, `I will not leave it off. If you want me to continue leading you (in prayer), I will do this; and if you all do not like it, I will leave you (i.e., I will stop leading you).’ They used to consider him to be of the best of them to lead them in prayer and they did not want anyone else to lead them other than him. So, when the Prophet came they informed him of this information and he said,
«يَا فُلَانُ، مَا يَمْنَعُكَ أَنْ تَفْعَلَ مَا يَأْمُرُكَ بِهِ أَصْحَابُكَ، وَمَا حَمَلَكَ عَلَى لُزُوم هَذِهِ السُّورَةِ فِي كُلِّ رَكْعَةٍ؟»
(O so-and-so! What prevents you from doing what your companions are commanding you to do, and what makes you adhere to the recitation of this Surah in every Rak`ah) The man said, `Verily, I love it.’ The Prophet replied,
«حُبُّكَ إِيَّاهَا أَدْخَلَكَ الْجَنَّة»
(Your love of it will cause you to enter Paradise.) This was recorded by Al-Bukhari, with a disconnected chain, but in a manner indicating his approval.
Al-Bukhari recorded from Abu Sa`id that a man heard another man reciting
﴿قُلْ هُوَ اللَّهُ أَحَدٌ ﴾
(Say: “He is Allah, One.”) and he was repeating over and over. So when morning came, the man went to the Prophet and mentioned that to him, and it was as though he was belittling it. The Prophet said,
«وَالَّذِي نَفْسِي بِيَدِهِ إِنَّهَا لَتَعْدِلُ ثُلُثَ الْقُرْآن»
(By He in Whose Hand is my soul, verily it is equivalent to a third of the Qur’an.) Abu Dawud and An-Nasa’i also recorded it. Another Hadith Al-Bukhari recorded from Abu Sa`id, may Allah be pleased with him, that the Messenger of Allah said to his Companions,
«أَيَعْجِزُ أَحَدُكُمْ أَنْ يَقْرَأَ ثُلُثَ الْقُرْآنِ فِي لَيْلَةٍ؟»
(Is one of you not able to recite a third of the Qur’an in a single night) This was something that was difficult for them and they said, “Which of us is able to do that, O Messenger of Allah” So he replied,
«اللهُ الْوَاحِدُ الصَّمَدُ ثُلُثُ الْقُرْآن»
(“Allah is the One, As-Samad” is a third of the Qur’an.) Al-Bukhari was alone in recording this Hadith.
Imam Malik bin Anas recorded from `Ubayd bin Hunayn that he heard Abu Hurayrah saying, “I went out with the Prophet and he heard a man reciting `Say: He is Allah, the One.’ So the Messenger of Allah said,
(It is obligatory.) I asked, `What is obligatory’ He replied,
(Paradise.)” At-Tirmidhi and An-Nasa’i also recorded it by way of Malik, and At-Tirmidhi said, “Hasan Sahih Gharib. We do not know of it except as a narration of Malik.” The Hadith in which the Prophet said,
«حُبُّكَ إِيَّاهَا أَدْخَلَكَ الْجَنَّة»
(Your love of it will cause you to enter Paradise.) has already been mentioned.
From Tafsir Ibn Kathir – The Reason for the Revelation of this Surah [Al-Ikhas] and its Virtues