Abu As-Sa'ib- the freed slave of Hisham bin Zuhrah-said:
"I heard Abu Hurairah say: 'The Messenger of Allah (ﷺ) said: "Whoever offers a prayer in which he does not recite Umm Al-Quran (Al Fatihah), it is deficient, it is deficient, it is deficient, incomplete." I (Abu As-Sa'ib) said: 'O Abu Hurairah, sometimes I am behind the Imam.' He poked me in the arm and said: 'Recite it to yourself, O Persian! For I heard the Messenger of Allah (ﷺ) say: "Allah says: "I have divided prayer between Myself and My slave into two halves, and My slave shall have what he has asked for.'" The Messenger of Allah (ﷺ) said: "Recite, for when the slave says: All the praises and thanks be to Allah, the Lord of all that exists, Allah says: 'My slave has praised Me.' And when he says: The Most Gracious, the Most Merciful, Allah says: 'My slave has extolled Me.' And when he says: The Only Owner (and the Only Ruling Judge) of the Day of Recompense (i.e. the Day of Resurrection), Allah says: 'My slave has glorified Me' . And when he says: You (alone) we worship, and You (alone) we ask for help (for each and everything), He says: 'This is between Me and My slave, and My slave shall have what he has asked for.' And when he says: 'Guide us to the straight way, the way of those on whom You have bestowed Your grace, not (the way) of those who earned Your anger, nor of those who went astray, He says: 'This is for My slave, and My slave shall have what he asked for.'"