(He) refers to Allah (swt), for He is the witness over human’s ungratefulness, denying and disbelieving. Allah (swt) says:

 ٰ﴾ وَاللَّهُ عَلَىٰ كُلِّ شَيْءٍ شَهِيدٌ﴿

 (and Allah is, over all things, Witness.) (Al-Mujadelah: 6)

Then Allah (swt) says as an answer to the oath about the human: