Tafsir Al-Jalalayn: At-Taghaabun, Ayah 18

(Knower of the invisible) i.e. that which is in the hearts of those who give alms of the feelings of boasting and fear (and the visible) He is Aware of their alms, (the Mighty) in retribution against those who boast about their alms or refuse to give alms, (the Wise) in His command and decree; it is also said that this means: the Wise in accepting alms and multiplying the reward of almsgiving; and it is also said this means: the Wise in that He enjoined His Messenger (pbuh) and his nation to divorce in accordance with the prophetic practice'.