Imam Al-Nawawi’s Riyad-us-Saliheen
Prohibition of passing in front of a Worshipper while he is offering Salat
1758. Abul-Juhaim `Abdullah bin Al-Harith (May Allah be pleased with him) said: The Messenger of Allah (sallallaahu alayhi wa sallam) said, “If the person who passes in front of a praying person, realizes the enormity of the sinfulness of this act, it will have been better for him to wait forty than to pass in front of him.”
[Al-Bukhari and Muslim].
[The narrator was not sure whether the Prophet (sallallaahu alayhi wa sallam) said forty days, months or years.]