Cain قابيل

Whoever sees him in a dream will transgress and kill a soul without right, because of His saying, the Exalted:

فَطَوَّعَتْ لَهُۥ نَفْسُهُۥ قَتْلَ أَخِيهِ فَقَتَلَهُۥ فَأَصْبَحَ مِنَ ٱلْخَـٰسِرِينَ

“And his soul permitted to him the murder of his brother, so he killed him and became among the losers.”

Quran 5:30 · Saheeh International

Whoever sees Cain and is not a killer will regret a deed he did, because of His saying, the Exalted:

فَبَعَثَ ٱللَّهُ غُرَابًا يَبْحَثُ فِى ٱلْأَرْضِ لِيُرِيَهُۥ كَيْفَ يُوَٰرِى سَوْءَةَ أَخِيهِ ۚ قَالَ يَـٰوَيْلَتَىٰٓ أَعَجَزْتُ أَنْ أَكُونَ مِثْلَ هَـٰذَا ٱلْغُرَابِ فَأُوَٰرِىَ سَوْءَةَ أَخِى ۖ فَأَصْبَحَ مِنَ ٱلنَّـٰدِمِينَ

“Then Allāh sent a crow searching [i.e., scratching] in the ground to show him how to hide the disgrace of his brother. He said, "O woe to me! Have I failed to be like this crow and hide the disgrace [i.e., body] of my brother?" And he became of the regretful.”

Quran 5:31 · Saheeh International