Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.077.
Section : Allah also strongly warns those who tamper with their prayers or are heedless.
Says Allah in the Qur’an, “Now there has succeeded them a later generation who have ruined their prayers and have followed lusts. But they will meet deception” (Maryam 59); “Ah, woe unto worshippers who are heedless of their prayers” (al-Ma’un 4-5).