Do not ever rejoice at someone else’s mistake
The commander of the faithful Imam Ali peace be upon him says:
لا تَبتَهِجَنَّ بِخَطاءِ غَيرِكَ؛ فإنَّكَ لَن تَملِكَ الإصابَةَ أبَداً.
‘Do not ever rejoice at someone else’s mistake, for verily you yourself will never be immune to committing mistakes.’
Source: Ghurar al-Hikam, no. 10294