Why is the reply "Thanks be to God" (الشكر لله) widespread in response to "Thank you" (شكراً), and what is the origin of this saying, knowing that "Whoever does not thank people does not thank God"?

Firstly: A Muslim should thank those who do him a favor, supplicate for them, and praise them. Many sacred texts encourage this, among them the saying of the Prophet, peace and blessings be upon him: "He who does not thank the people does not thank Allah."

Secondly: A Muslim's benevolence towards people should be purely for the sake of Allah the Almighty, not seeking recompense or gratitude from them, as stated in His saying, may He be exalted: {We feed you only for the countenance of Allah. We wish not from you reward or gratitude.}

Thirdly: Saying "thanks be to Allah" to someone who thanks you is permissible if the intention is humility towards Allah and attributing the favor back to Him, Glorified be He, not to negate thanking people. What is recommended is combining thanks to Allah with thanks to the benefactor.