Tafsir of Al-Adiyat 100:7

And to that He bears witness. Qatadah and Sufyan Ath-Thawri both said, "And indeed Allah is a witness to that.'' It is also possible that the pronoun (He) could be referring to man. This was said by Muhammad bin Ka`b Al-Qurazi. Thus, its meaning would be that man is a witness himself to the fact that he is ungrateful. This is obvious in his condition, meaning this is apparent from his statements and deeds. This is as Allah says,

ما كان للمشركين أن يعمروا مساجد الله شهدين على أنفسهم بالكفر

It is not for the idolators, to maintain the Masajid (Mosques) of Allah, while they witness disbelief against themselves. (9:17) Allah said;

وإنه لحب الخير لشديد