(18) باب فِي سُورَةِ الصَّمَدِ
Abu Sa'id al-Khudri said:
A man heard another man reciting "Say, He is Allah, One" He was repeating it. When the next morning came, he went to the Messenger of Allah (ﷺ) and mentioned to him. The man tool it (this surah) as a small one. The Prophet (ﷺ) said: By Him in Whose Hand is my life, it is equivalent to a third of the Qur'an.
Reference: Sunan Abi Dawud 1461
In-book reference: Book 8, Hadith 46
English translation: Book 8, Hadith 1456