Surah 100. Al-Adiyat, Ayah 6

I.e., whenever he surrenders to his appetites, symbolised by the madly storming chargers, he forgets God and his own responsibility to Him.

Man, i.e., unregenerate man, in contrast to those who receive guidance and wage unceasing war with Evil, is ungrateful to his Lord and Cherisher, Him Who created him and sustains him, and sends His blessings and favours at all times. The ingratitude may be shown by thoughts, words, and deeds,-by forgetting or denying Allah and His goodness, by misusing His gifts, or by injustice to His creatures.