Sahih Muslim Book - 4, Hadith - 1132

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ أَبِى النَّضْرِ عَنْ بُسْرِ بْنِ سَعِيدٍ أَنَّ زَيْدَ بْنَ خَالِدٍ الْجُهَنِىَّ أَرْسَلَهُ إِلَى أَبِى جُهَيْمٍ يَسْأَلُهُ مَاذَا سَمِعَ مِنْ رَسُولِ اللَّهِ -صلى الله عليه وسلم- فِى الْمَارِّ بَيْنَ يَدَىِ الْمُصَلِّى قَالَ أَبُو جُهَيْمٍ قَالَ رَسُولُ اللَّهِ -صلى الله عليه وسلم- « لَوْ يَعْلَمُ الْمَارُّ بَيْنَ يَدَىِ الْمُصَلِّى مَاذَا عَلَيْهِ لَكَانَ أَنْ يَقِفَ أَرْبَعِينَ خَيْرًا لَهُ مِنْ أَنْ يَمُرَّ بَيْنَ يَدَيْهِ ». قَالَ أَبُو النَّضْرِ لاَ أَدْرِى قَالَ أَرْبَعِينَ يَوْمًا أَوْ شَهْرًا أَوْ سَنَةً.

It was narrated from Busr bin Sa'eed that Zaid bin Khalid Al-Juhani sent him to Abu Juhaim to ask him what he heard from the Messenger of Allah (s.a.w) about one who passes in front of a person who is praying. Abu Juhaim said: "The Messenger of Allah (s.a.w) said: 'If the one who passes in front of one who is praying knew what (sin) he incurs, he would realize that waiting for forty is better than passing in front of him."' Abu An-Nadr said: "I do not know whether he said forty days, or months, or years."