"And the day the wrongdoer will bite on his hands" meaning: Ubayy ibn Khalaf. "He will say" meaning: he will bite them in remorse.
Mujahid said: Ubayy ibn Khalaf used to attend the Prophet, peace be upon him, and Uqbah ibn Abi Mu'ayt discouraged him from doing so. This is what Ubayy ibn Khalaf will say in the Hereafter: "Oh, I wish I had taken with the Messenger" meaning: Muhammad, "a way" meaning: to Allah by following him.
﴿وَيَوْم يعَض الظَّالِم﴾ يَعْنِي: أُبَيَّ بْنَ خَلَفٍ ﴿عَلَى يَدَيْهِ﴾ أَيْ: يَأْكُلُهَا نَدَامَةً.
قَالَ مُجَاهِدٌ: كَانَ أُبَيُّ بْنُ خَلَفٍ يَحْضُرُ النَّبِي عليه السلام فَزَجَرَهُ عُقْبَةُ بْنُ أَبِي مُعَيْطٍ عَنْ ذَلِكَ، فَهُو قَوْلُ أُبَيِّ بْنِ خَلَفٍ فِي الْآخِرَةِ. ﴿يَا لَيْتَني اتَّخذت مَعَ الرَّسُول﴾ يَعْنِي: مُحَمَّدًا ﴿سَبِيلا﴾ إِلَى الله باتباعه
