Nasai

(1) In this hadith, the word "tasaddaqū" is used, but what is meant is not obligatory (fard) or voluntary (nafl) charity, rather, what is intended is spending in general. The subtlety in this word is that a believer is rewarded even for his obligatory expenditures, provided that he spends from lawful (halal) wealth and has the intention of obeying Allah and seeking reward from Him.

(2) In some ahadith, children are mentioned before the wife. There is no difference, because the expenses for both are equally obligatory.

(3) From the order mentioned, it is understood that until the obligatory expenditures are fulfilled, one should not give charity beyond that. First yourself, then others. Except in cases where one has no choice, for example: if a guest arrives at the house, then even by keeping the household hungry, hospitality can be shown to the guest. Thus, what is being discussed here is voluntary charity by choice.

(4) "You know best." That is, then it is your discretion. Spend wherever you deem appropriate.

1691. English Commentary:
➊ The Prophet sallallahu alayhi wa sallam has described spending on oneself and on one’s loved ones as charity (sadaqah). That is, on the basis of good intention, a person receives the reward of charity from Allah even for these obligatory expenditures.
➋ And in this order, priority and importance have been given to one’s own self. Because when a person’s own health is sound and strength is maintained, only then can he exert effort and labor for others as well.
➌ There is also an indication here for the family members: due to earning and striving, the husband and father are given priority and precedence.
➍ And the same ruling applies to that woman upon whose shoulders the expenses of the household or children have fallen.

Lexical Explanation 513:
تَصَدَّقْ بِىہ عَلٰی نَفسِکَ — "تَصَدَّقْ" is used here in the meaning of "أَنفِقْ" (spend), that is, spend it on yourself. By using the word "charity" (sadaqah) and intending "spending," the purpose is to indicate that spending on those who have rights over you is equal in reward and merit to giving charity.
أَنتَ أَبصَر — meaning, you have more knowledge as to who among those on whom you spend is more deserving; or it means that now it depends on your own discretion—if you wish, you may spend it, and if you wish, you may keep it with yourself.

Benefit 513:
From this hadith, it is understood that a person spending on himself within the limits set by the Shari‘ah also carries reward just like giving charity and alms. The order is stated as follows: first on oneself, then on one’s children, then on one’s wife, and then on one’s servant. Whatever remains is left to his discretion—if he wishes, he may spend it somewhere, or if he wishes, he may keep it with himself so that it may be of use in the future. Therefore, it is established that spending according to the order of those who have rights is obligatory, so that the right of any deserving person is not violated.

Takhrij:
«أخرجه أبوداود، باب في صلة الرحم، حديث:1691، والشافعي في مسنده:2 /64، والنسائي، الزكاة، حديث:2536، والحاكم: 1 /415.»©Explanation:
In this hadith, it is mentioned what the order of priorities should be when spending wealth. Thus, it is stated: the very first right upon a person is that of his own self. After that, he should spend according to the order mentioned in this hadith, and finally, when it is said: «أَنْتَ أَعْلَمُ» and in another narration «أَنْتَ أَبْصَرُ» as well, its meaning is that spending in these avenues is the prescribed (shar‘i) order; after that, he himself knows best who is more deserving and in need.

Benefit:
From this hadith it is established upon whom expenditure should be made; the Shariah has also prescribed their ranks: first upon oneself, then upon one's children, then upon one's household, then upon one's servant. If there is still capacity, then one may give to whomever is deemed deserving. Those people are mistaken who leave their own hungry and spend on others.