How does fasting differ from other acts of worship, given that all acts of worship are for Allah and He is the One Who rewards for them, especially since Allah said in the Hadith Qudsi about fasting: "Fasting is for Me, and I shall reward for it"?

The Hadith Qudsi states: "Every deed of the son of Adam is for him, except fasting; it is for Me, and I shall reward for it." This is an authentic hadith narrated by Al-Bukhari and Muslim.

Al-Nawawi mentioned several interpretations of the meaning of "it is for Me, and I shall reward for it": - It was said because fasting is an act of worship by which no one but Allah has been worshipped. - And it was said because it is far from ostentation due to its hidden nature. - And it was said because the fasting person and his soul have no share in it. - And it was said that Allah Almighty alone knows its reward. - And it was said that it is an addition of honor.

There is no contradiction between these statements, and it is possible that all of them are intended. And any act of worship intended for other than Allah will bring no reward to its doer.