Sayyiduna Abu Sa’id bin Mu’alla (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) passed by me while I was (praying) in the mosque. The Prophet (peace be upon him) called me, but I did not come (and continued my prayer). Then when I came to the Prophet (peace be upon him), he said: “Why did you not come to me?” I replied, “I was praying.” The Prophet (peace be upon him) said: “Did Allah not say” « يَاأَيُّهَاالَّذِينَآمَنُوااسْتَجِيبُوالِلَّهِوَلِلرَّسُولِإِذَادَعَاكُمْلِمَايُحْيِيكُمْ »[ سورة الأنفال : 24 ] “O you who believe! Respond to Allah and to the Messenger when he calls you to that which gives you life.” Then he said: “Shall I not teach you the greatest Surah of the Qur’an before you leave the mosque?” So when the Prophet (peace be upon him) was about to leave the mosque, I reminded him. The Prophet (peace be upon him) said: “« الْحَمْدُلِلَّهِرَبِّالْعَالَمِينَ » that is (Surah Al-Fatihah), the seven oft-repeated verses (As-Sab’ul Mathani), and this is the Great Qur’an which has been given to me.”
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الكلام المباح فى الصلاة والدعاء والذكر، ومسألة الرب عز وجل وما يضاهي هذا ويقاربه / 862