Imam Muhammad Baqir (a.s.) says:
“One day the Messenger of Allah was sitting in the Mosque when a person entered and started praying. But he did not perform the Rukū’ and Sajdahs properly (he did not recite the Wajib formulas or did so incorrectly, or he might not have remained still or failed to maintain composure during recitation or movements)
The Messenger of Allah (S) said, He (this man) touches his forehead to the ground like a crow pecks at the earth and lifts it. If he dies praying like this he would not die on my religion.”18
The Messenger of Allah (S) said,
“The greatest thief is one who steals in his Prayer.” Someone asked him, “O Messenger of Allah! How could one steal in his Prayer?” He (S) replied,
“It is not performing the Rukū’ and Sajdahs of Prayers properly.”19
He (S) also said,
“The prayer of one who does not performs Rukū’ and sajdah properly is invalid.”20
The Holy Prophet (S) also said,
“The prayer of one who performs Rukū’ and as-Sajda properly goes up in a condition of illumination and splendour. The doors of heaven open wide to accept it and the Prayer says, ‘You have protected me, may Allah (S.w.T.) protect you. The angels say, ‘Mercy and Grace of Allah be on the one who has performed this prayer. But if the prayer is not performed properly it rises up in a state of darkness and the door of heaven slams on it and the prayer says, ‘You have wasted me, may Allah waste you.’ And the Prayer is thrown at his face.”21
Allah’s Messenger (S) also stated,
“Everything has a face. (The most important part of a body). And the face of your religion is Prayer. Then none of you should deface and destroy his Prayer. (Which like the face is to the body, it is to ones religion).”22