Sayyidina Abu Huraira, may Allah be pleased with him, narrated that the Beloved Prophet, may Allah’s peace and blessings be upon him, said:
“A prayer performed by someone who has not recited the Essence of the Quran¹ during it is deficient (and he repeated the word three times), incomplete.”
Someone said to Sayyidina Abu Huraira: “[Even though] we are behind the imam?”²
He said: “Recite it to yourself, for I have heard the Prophet, may Allah’s peace and blessings be upon him, say that Allah, glorified be He, had said:
“I have divided prayer between Myself and My servant into two halves, and My servant shall have what he has asked for.
When the servant says: Al-hamdu lillahi rabbil 'alaamīn (Praise be to Allah, Lord of the Worlds), Allah says: My servant has praised Me
And when he says: Ar-rahmanir-rahīm (The Merciful, the Compassionate), Allah says: My servant has extolled Me,
And when he says: Maaliki yawmid-dīn (Master of the Day of Judgement), Allah says: My servant has glorified Me - and on one occasion He said: My servant has submitted to My power.
And when he says: Iyyaka na'budu wa iyyaka nasta'īn (It is You we worship and it is You we ask for help), He says: This is between Me and My servant, and My servant shall have what he has asked for.
And when he says: Ihdinas-siraat al mustaqīm, siraatal ladhīna an 'amta alayhim ghayril-maghdubi 'alayhim wa lad-daallin (Guide us to the Straight Path, the Path of those upon whom You have bestowed favors, not of those against whom You are angry, nor of those who are astray), He says: This is for My servant, and My servant shall have what he has asked for.”
[Related by Muslim (also by Malik, Tirmidhi, Abu Dawud, an-Nasa'i and Ibn Majah)]