Hazrat Shaikh Moulana Muhammad Zakariyya (rahmatullahi ‘alaih) once mentioned the following:
Experience has shown that if a person makes the decision to set aside a certain amount of wealth to spend in the path of Allah Ta‘ala, then he will continue to find avenues of goodness and opportunities to spend the wealth for the sake of Allah Ta‘ala.
On the contrary, if a person thinks to himself, “When I find an opportunity to spend, then at that time, I will see if I have the wealth,” then the first problem is that when a person thinks in this manner, he will find very few occasions which he will consider important for spending his wealth. Whenever an opportunity to spend in the path of Allah Ta‘ala presents itself, his nafs and Shaitaan will place the thought in his heart that this avenue is not an important and necessary avenue, hence he should not spend his wealth in this avenue.
In the case where such an opportunity arises wherein spending the wealth is vitally important, then in most instances, he will find that at that time, he will not possess the money to spend. Even if he does possess the money to spend, he will think of his own, personal needs, and hence his heart will desire to spend the least amount of wealth in sadaqah.
However, at the very beginning of the month, after a person has received his salary, if he sets aside a stipulated amount of wealth, or on a daily basis, he takes a stipulated portion of the income from his business and sets it aside in a separate box, solely to be spent in the path of Allah Ta‘ala, then when he finds an opportunity to spend for the sake of Allah Ta‘ala, he will not find any reluctance in his heart to spend the wealth. The reason is that he understands that in all cases, this amount has to be spent in the path of Allah Ta‘ala.
This is a tried and tested prescription for those who wish to spend in the path of Allah Ta‘ala. If one wishes, he may try it for a few days and see how effective it is.
(Fazaail-e-Sadaqaat [Urdu] – 1/74)