The seven ahruf

Al-Bukhari transmits the Prophet ﷺ's saying that the Qur'an was revealed in seven ahruf (modes), so that whatever is easy of it may be recited. ¹

It was transmitted by Umar, when he heard Hisham ibn Hakim reciting Surat al-Furqan differently from his own recitation. He led him to the Prophet, who had each of them recite, and said to each that it had been revealed in that form. ¹

Scholars differ widely on what is meant by the seven ahruf. Some counted them as seven aspects: command and prohibition, promise and warning, disputation, narratives, and parables. Others took them to be differences in vowelling, omission, anticipation and postponement, and substitution. Others linked them to the readings of the Arab tribes. The question is among the most delicate in the sciences of the Qur'an. The attribution of each view to its author would need a further source.

The hadith is linked to Umar ibn al-Khattab. ¹