Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever prays a prayer in which he does not recite Umm al-Qur'an, that prayer is deficient, it is deficient, it is deficient." Abu al-Sa'ib (may Allah have mercy on him) said: I said to Sayyiduna Abu Hurayrah (may Allah be pleased with him): Sometimes I am behind the imam. He pressed my arm and said: O Persian! Recite it within yourself, for I heard the Messenger of Allah (peace and blessings be upon him) say that Allah Almighty says: "I have divided the prayer between Myself and My servant into two halves; half of it is for Me and half of it is for My servant, and My servant shall have what he has asked for. When the servant says: 'All praise is for Allah, the Lord of all the worlds' [Surah al-Fatihah: 2], Allah Almighty says: My servant has praised Me. When the servant says: 'The Most Gracious, the Most Merciful' [Surah al-Fatihah: 3], Allah Almighty says: My servant has extolled Me. When the servant says: 'Master of the Day of Judgement' [Surah al-Fatihah: 4], Allah Almighty says: My servant has glorified Me, and this verse is between Me and My servant. When the servant says: 'You alone we worship and You alone we ask for help' [Surah al-Fatihah: 5], Allah Almighty says: This is between Me and My servant, and the end of the surah is for My servant, and My servant shall have what he has asked for. When the servant says: 'Guide us to the straight path' [Surah al-Fatihah: 6], to the end of the surah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3952