The Prophet (ﷺ) said: "Say: He is Allah, (the) One" is one-third of the Quran."
Sunan an-Nasa'i Book 11, Hadith 121
← Previous Hadith A man heard another man reciting "Say: He is Allah, (the) One" and repeating it. When morning came he went to the Messenger of Allah (ﷺ) and told him about that. The Messenger of Allah (ﷺ) said: "By the One in Whose Hand is my soul, it is equal to one-third of the Quran."

Sunan an-Nasa'i Book 11, Hadith 120 Next Hadith → "Muadh stood up and prayed Isha', and made it lengthy. The Prophet (ﷺ) said: 'Do you want to cause hardship to the people, O Mu'adh; do you want to cause hardship to the people O Mu'adh? Why didn't you recite 'Glorify the Name of your Lord Most High' or Ad-Duha or; 'When the heaven is cleft asunder?"

Sunan an-Nasa'i Book 11, Hadith 122