Narrated Abu Sa'id bin Al-Mu'alla: While I was praying in the Mosque, Allah's Messenger ﷺ called me but I did not respond to him. Later I said, "O Allah's Messenger ﷺ! I was praying". He said, "Didn't Allah say'--"Give your response to Allah (by obeying Him) and to His Apostle when he calls you". (8:24) He then said to me, "I will teach you a Sura which is the greatest Sura in the Qur'an, before you leave the Mosque". Then he got hold of my hand, and when he intended to leave (the Mosque), I said to him, "Didn't you say to me, 'I will teach you a Sura which is the greatest Sura in the Qur'an?' He said, "Al-Hamdu-Li l-lah Rabbi-l-'alamin (ie Praise be to Allah, the Lord of the worlds) which is Al-Sab'a Al-Mathani (ie seven repeatedly recited Verses) and the Grand Qur'an which has been given to me".