Ibn Abbas narrated: A beautiful woman, from among the most beautiful of women, used to pray behind the Prophet. Some of the people used to go to pray in the first row to ensure they would not be able to see her. Others would pray in the last row of the men, and they would look from underneath their armpits [in rukoo’ and sujood] to see her. Because of this act, in regard to her, Allah revealed, “Verily We know the eager among you to be first, and verily We know the eager among you to be behind.” (Surah al-Hijr ayah 24)
(Ibn Majah, Abu Dawud Tayalisi, Baihaqi, Ahmad, Tirmidhi, and Nasai and it is judged sahih by Albani. He includes it as #2472 in his Silsilat al-Ahadith as-Sahih)
Why is this narration so fascinating? Because it reveals how even in the time of RasulAllah (sallAllahu ‘alayhi wa sallam), the Sahabah had differing levels of emaan and even in salah - a time when all worldly desires are meant to be put aside - they still acted upon their desires.
Yet to me, the most interesting part of this narration is that when Allah sent down a revelation concerning this situation, He did not rebuke the woman - He rebuked the men who forgot their khushoo’, the men who forgot that Allah is Ever-Watching, the men who forgot that Allah can easily expose those who claim piety yet act in a contrary manner. Allah is the One Who reminded these men that their intentions are fully known to Him.