Hadith: If the person passing in front of someone praying knew the extent of the guilt he is incurring, he would prefer to stand for forty rather than pass in front him. Abu An-Nadr said: I am not sure if he said forty days, months, or years

عن أبي جُهَيْمِ بنُ الْحَارِثِ بْنِ الصِّمَّةِ الأنصاري رضي الله عنه مرفوعًا: «لو يَعْلم المارُّ بين يَدَي الْمُصَلِّي ماذا عليه من الإثم؟ لكان أن يَقِفَ أربعين خيرًا له من أن يَمُرَّ بين يديه»، قال أَبُو النَّضْرِ: لا أدري: قال أربعين يومًا أو شهرًا أو سنةً.
[صحيح] - [متفق عليه]

Abu Juhaym ibn al-Hārith ibn As-Simmah al-Ansāri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "If the person passing in front of someone praying knew the extent of the guilt he is incurring, he would prefer to stand for forty rather than pass in front him." Abu An-Nadr said: "I am not sure if he said forty days, months, or years."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

The praying person is standing before his Lord, the Almighty, supplicating Him privately and calling upon Him. If someone passes in front of him while being in this state, he will interrupt his private supplication and disturb his worship. That is why it has become a great sin to disturb the Muslim’s prayer by passing in front of him. So, the Prophet (may Allah's peace and blessings be upon him) informed us that if one knew the sin and misdeed earned from such an act, he would prefer to stand in his place for 'forty' rather than pass in front of someone praying. Therefore, a Muslim should beware of this act and avoid doing it. The narrator was unsure of what was meant by 'forty': are they forty days, months, or years? However, the number mentioned is not intended to restrict it to a certain period of time; rather, it is intended to emphasize the prohibition.