People with a bier passed by the Messenger of Allah ﷺ. They (the companions) spoke highly of him. He said: Paradise is certain for him. Then some people with another (bier) passed by him. They spoke very badly of him. He said: Hell is certain for him. He then said: Some of you are witness to others.  

مَرُّوا عَلَى رَسُولِ اللَّهِ ﷺ بِجَنَازَةٍ فَأَثْنَوْا عَلَيْهَا خَيْرًا فَقَالَ وَجَبَتْ ثُمَّ مَرُّوا بِأُخْرَى فَأَثْنَوْا عَلَيْهَا شَرًّا فَقَالَ وَجَبَتْ ثُمَّ قَالَ إِنَّ بَعْضَكُمْ عَلَى بَعْضٍ شُهَدَاءُ