Sunan at-Tirmithiy كتاب الصلاة باب ما جاء فى تأخير صلاة العصر
Jābir Ibn-'Abdullāh said, "Whoever prays a unit of prayer without reciting the cornerstone of the Qur'ān (1) has not prayed, unless he is praying behind the Imām." Footnote: Whoever prays a unit of prayer without reciting the cornerstone of the Qur'ān (1) has not prayed, unless he is praying behind the imām." Footnote (1): 1. Al-Fātiḥah: the opening chapter in the Qur'ān. Click on ḥadīth to read more