Imâm-i Rabbânî ‘quddisa sirruh’ states as follows in the 17th letter of the third volume of his book Maktûbât:
He who does favours is to be thanked and respected. Therefore, it is a human duty for every man to thank Allâhu ta’âlâ, who has bestowed these favours. It is a debt, a duty which wisdom commands. But it is not easy to carry out this thanksgiving due to Him, for men, having been originally created out of nothing, are weak, indigent, faulty and defective. As for Allâhu ta’âlâ, He always and eternally exists. He is quite far from defectiveness. Every kind of superiority belongs to Him only. Men have by no means any similarity or proximity to Allâhu ta’âlâ. Can men, who are so inferior, thank such a high being as Allâhu ta’âlâ in a manner worthy of His Dignity? There are so many things that men consider beautiful and precious, but He knows that they are evil and dislikes them. Things which we consider to be reverence or thanks may be lowly things not liked at all. For this reason, men, with their own defective minds and short sights, cannot discern the things that express thanks and veneration to Allâhu ta’âlâ. Unless the ways of thanking and respecting Allâhu ta’âlâ are shown by Him, acts that are considered as praising may be slanders.
So, the gratitude to be shown and the human duties to be done towards Allâhu ta’âlâ with the heart, tongue and body were defined by Allâhu ta’âlâ and communicated by His beloved Prophet ‘sall-Allâhu ta’âlâ ‘alaihi wa sallam’! The human duties which Allâhu ta’âlâ showed and ordered are called Islam. One thanks Him by following the way His Prophet taught. Allâhu ta’âlâ does not accept or like any thanks, any worship incompatible with or outside of this way, because there are many things which men consider beautiful but which Islam disapproves of and regards as ugly.