If someone is having severe financial difficulties, the halachic authorities write that one may rely and use the money he has separated for the food for children over the age of six. Even when doing this, however, one must make an exact calculation of this money and use it or the food of his children above this age.
One who wants to fulfil all of the laws appertaining to the tithing of one’s money, should study the laws in a holy book, or ask a Rabbi how to conduct himself in this matter, and he will then be successful in all his ways. In order not to err in these matters, when he commences separating these tithes he should say clearly that he is not doing it as a vow or a promise. He should nevertheless be very careful to fulfil this law, and not stop even if it is very hard for him, and Hashem will send him blessings in everything that he does.
