Is a Muslim sinful if he gives charity with the intention that Allah will compensate him in this world before the Hereafter, to help him marry, despite his knowledge that he commits many sins? And is this considered a bad assumption about Allah?

Allah replaces expenditures made in His cause and spends upon those who spend, as confirmed by His words: "And whatever you spend of anything, He will replace it; and He is the best of providers." And the Qudsi Hadith is authentically reported: "Spend, O son of Adam, and I shall spend on you." Maintaining kinship ties increases provision and prolongs life, as stated in the Hadith: "Whoever wishes that his provision be expanded for him or his life span be prolonged, let him maintain his ties of kinship." Therefore, seeking provision and a long life through maintaining kinship ties and giving charity is not blameworthy. Hence, whoever gives charity with the intention of receiving compensation for marriage is not sinful, though it is better for a Muslim to seek Allah's countenance through his deeds.