عَنْ كَعْبِ بْنِ عِيَاضٍ قَالَ طَعَنْتُ عَلٰى عَلِيٍّؑ بَيْنَ يَدَيْ رَسُولِ اللّهِ ﷺ فَوَكَزَنِي فِي صَدْرِي ثُمَّ قَالَ يَا كَعْبُ اِنَّ لِعَلِيٍّؑ نُورَيْنِ نُوراً فِي السَّمَاءِ وَ نُوراً فِي الْاَرْضِ فَمَنْ تَمَسَّكَ بِنُورِهِ اَدْخَلَهُ اللهُ الْجَنَّةَ وَ مَنْ اَخْطَاَهُ اَدْخَلَهُ النَّارَ فَبَشِّرِ النَّاسَ عَنِّي بِذٰلِكَ
Ka’b Ibn Eyaaz reports, “I criticized Ali in front of the Messenger of Allah (peace be upon him and his holy progeny). So he (peace be upon him and his holy progeny) boxed me in my chest and said,
‘O Ka’b! Surely for Ali (peace be upon him) there are two lights; one light in the sky and the other in the earth. Whoever fastens unto his light, Allah will make him enter paradise and whoever finds faults with him, Allah will make him enter hell. So give glad tidings to the people from my side about this.”
Note:
Please bear in mind that the Holy Prophet (peace be upon him and his holy progeny) was at the highest pinnacle of ethics. And yet he (peace be upon him and his holy progeny) boxed Ka’b for this act of insolence. وكز means to box as has come in the Holy Quran فَوَكَزَهُ مُوسى فَقَضى عَلَيْهِ (Surah Qasas: Verse 15) “So Musa boxed him and killed him.”
Also remember that the Messenger of Allah (peace be upon him and his holy progeny) does not do anything from his side. If he (peace be upon him and his holy progeny) has boxed Ka’b, then you can imagine what Allah the High will do to this insolent fool?
Light in the skies means for the angels. Ali (peace be upon him) is a source of guidance for them. So whoever fastens to the light of guidance of Ali (peace be upon him), Allah the Merciful will cause him to enter him paradise.
The Holy Prophet (peace be upon him and his holy progeny) also ordered him to spread this narration among the people.
References
1. Behaar al-Anwaar, vol. 23, p. 319, H. 34
2. Taveel al-Aayaat al-Zaaherah