Reference: Siyar A’laam an-Nubalaa
Abu Nadhrah رحمه الله reports that said:
They struck him (‘Uthmaan ibn ‘Affaan) and [his] blood spilt onto the mus.haf, [specifically] on the aayah:
{And Allaah will be sufficient for you against them. And He is the All-Hearing, the All-Knowing}, al-Baqarah 2:137
