Sufyan on Salat: Reverence is required for sound prayer

Bishr ibn al-Harith reported: Sufyan al-Thawri, may Allah have mercy on him, said, “Whoever does not have reverence has spoiled his prayer.”

Source: Qūt al-Qulūb 2/161

عن بشر بن الحارث قال قال سفيان الثوري رحمه الله من لم يخشع فسدت صلاته

2/161 قوت القلوب في معاملة المحبوب