There is a beautiful verse in the Quran,
وَيَسْأَلُونَكَ مَاذَا يُنفِقُونَ قُلِ الْعَفْوَ
‘They ask you, O my dear Prophet, what they should spend? Tell them, the excess.’ The question asked by the Muslims was, what should we spend? Allah gives the answer, say, “the excess”. Now how do you define the excess? You are earning ten thousand but your expenditure is ten thousand plus. You say, “I have to borrow some money every month. My family does not run!” Another fellow who earns two thousand taka but he runs his family in such a manner that he spends every month five hundred taka for the poor people in his village. Islam leaves it upon the person. He has been given the full freedom to earn but at the same time he is asked by his creator spend your excess for the poor. Islam does not force something but it asks you in a manner appealing to your intellect.