Musannaf Ibn Abi Shayba 33:1060

Ishaq ibn Mansur narrated to us, he said: Al-Hakam ibn Abd al-Malik narrated to us, from Qatadah, from Mutarrif ibn al-Shikhkhir, from Ibn Abbas regarding [the verse]: "From festering water" (min ma'in sadid). He said: It is what flows between the skin of the disbeliever and his flesh.