And this monotheism, which is the foundation of religion, is the greatest justice. Its opposite, associating partners with Allah, is the greatest injustice. As al-Bukhārī and Muslim reported in their Sahīhs, ‘Abd Allāh ibn Mas‘ūd said:

“When this verse was revealed, ‘Those who believe and do not mix their faith with wrongdoing,’ it weighed heavily upon the Prophet’s Companions, and they said, ‘Which of us has not wronged himself?’ He replied, ‘Have you not heard the words of the righteous servant: “Indeed, associating partners with Allah is a tremendous wrong”?’”

Also in the two Sahīhs, Ibn Mas‘ūd said:

“I said, ‘O Messenger of Allah, which sin is greatest?’ He replied, ‘To set up a rival to Allah when He created you.’ I asked, ‘Then which?’ He replied, ‘Then to kill your child for fear that he will eat with you.’ I asked, ‘Then which?’ He replied, ‘To commit adultery with your neighbour’s wife.’ Allah then revealed in confirmation of this: ‘And those who do not invoke another god besides Allah, nor kill a soul whose killing Allah has forbidden, except with just cause, nor engage in unlawful sexual intercourse’—to the end of the verse.”

The following has been reported from more than one of the early generations, and has also been narrated as a report traced back to the Prophet:

“There are three registers of wrongdoing: a register from which Allah forgives nothing, a register in which Allah leaves nothing unsettled, and a register to which Allah pays no heed at all. As for the register from which Allah forgives nothing, it is associating partners with Him, for Allah does not forgive the association of partners with Him. As for the register in which Allah leaves nothing unsettled, it is people’s wrongdoing against one another, for Allah will certainly secure justice for the wronged against the wrongdoer. As for the register to which Allah pays no heed at all, it is the servant’s wrongdoing against himself in matters between himself and