جامع الترمذي

Narrated Abu Hurairah: that the Messenger of Allah (ﷺ) came out to Ubayy bin Ka'b, and the Messenger of Allah (ﷺ) said: "O Ubayy!" And he was performing Salat, so Ubayy turned around but he did not respond to him, so Ubayy finished his Salat quickly. Then he turned to the Messenger of Allah (ﷺ) and said: 'As-Salamu 'Alaikum, O Messenger of Allah!' The Messenger of Allah (ﷺ) said: 'Wa 'Alaikum As-Salam - what prevented you from responding to me when I called you Ubayy?' He said: 'O Messenger of Allah! I was performing Salat.' So he said: 'Do you not find among what Allah revealed to me: Respond to Allah and to the Messenger when they call you to what gives you life?' He said: 'Of course, I shall not repeat that, if Allah wills.' He said: 'Would you like for me to teach you a Surah the likes of which has neither been revealed in the Tawrah, nor the Injil, nor the Zabur, nor in the entire Qur'an?' He said: "Yes, O Messenger of Allah!' The Messenger of Allah (ﷺ) said: 'What do you recite in your Salat?' He said: 'I recite Umm Al-Qur'an.' So the Messenger of Allah (ﷺ) said: 'By the One in Whose Hand is my soul! The like of it has neither been revealed in the Tawrah, nor the Injil nor the Zabur, nor in the Furqan. It is the seven oft-repeated, and the Magnificent Qur'an which I was given.'"