Sahih Bukhari Volume 2, Book 23, Hadith 1368

حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ صُهَيْبٍ، قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ ـ رضى الله عنه ـ يَقُولُ مَرُّوا بِجَنَازَةٍ فَأَثْنَوْا عَلَيْهَا خَيْرًا، فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ وَجَبَتْ ‏"‏‏.‏ ثُمَّ مَرُّوا بِأُخْرَى فَأَثْنَوْا عَلَيْهَا شَرًّا فَقَالَ ‏"‏ وَجَبَتْ ‏"‏‏.‏ فَقَالَ عُمَرُ بْنُ الْخَطَّابِ ـ رضى الله عنه ـ مَا وَجَبَتْ قَالَ ‏"‏ هَذَا أَثْنَيْتُمْ عَلَيْهِ خَيْرًا فَوَجَبَتْ لَهُ الْجَنَّةُ، وَهَذَا أَثْنَيْتُمْ عَلَيْهِ شَرًّا فَوَجَبَتْ لَهُ النَّارُ، أَنْتُمْ شُهَدَاءُ اللَّهِ فِي الأَرْضِ ‏"‏‏

Narrated By Anas bin Malik : A funeral procession passed and the people praised the deceased. The Prophet said, "It has been affirmed to him." Then another funeral procession passed and the people spoke badly of the deceased. The Prophet said, "It has been affirmed to him". 'Umar bin Al-Khattab asked (Allah's Apostle (p.b.u.h)), "What has been affirmed?" He replied, "You praised this, so Paradise has been affirmed to him; and you spoke badly of this, so Hell has been affirmed to him. You people are Allah's witnesses on earth."