For how long does a father have to spend on his child?
Question

My sister’s son came to live with me after living with his father, and I agreed to that on condition that he send me a monthly sum of 500 riyals. After a while he stopped sending the money and claimed that his son was not doing anything good for him because he was so far away from him, and that we should meet all his needs of food, drink, clothing, marriage, a car and so on. His father refused to send his son’s medical file for him to receive treatment at the expense of the company for which he works. Do we have the right, according to sharee’ah, to demand that he spend on his son who is now 16 years old and is studying in high school?.
Praise be to Allah.A man is obliged to spend on his parents and children if they are in need and are poor. 
Al-Khuraqi (may Allah have mercy on him) said: 
A man is obliged to spend on his parents and on his children – male and female – if they are poor and he has enough to spend on them. 
Ibn Qudaamah said:  
The basic principle is that a man is obliged to spend on his parents and children, according to the Quran and Sunnah and scholarly consensus. 
With regard to the Quranic evidence, Allah says (interpretation of the meaning): 
“Then if they give suck to the children for you, give them their due payment”
[al-Talaaq 65:6] 
So the payment for breastfeeding the child is incumbent upon the father.  
And Allah says (interpretation of the meaning): 
“but the father of the child shall bear the cost of the mother’s food and clothing on a reasonable basis”
[al-Baqarah 2:233]
And Allah says (interpretation of the meaning): 
“And your Lord has decreed that you worship none but Him. And that you be dutiful to your parents”
[al-Isra’ 17:23]
Being dutiful includes spending on them if they are in need. 
Evidence from the Sunnah includes the words of the Prophet (peace and blessings of Allah be upon him): “Take what is sufficient for you and your child, on a reasonable basis.” Agreed upon. 
‘Aa’ishah narrated that the Prophet (peace and blessings of Allah be upon him) said: “The best of what a man consumes is what he earns, and his children are part of his earnings.” Narrated by Abu Dawood, 3528; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel. 
With regard to scholarly consensus: 
Ibn al-Mundhir said: The scholars are unanimously agreed that spending on poor parents who have no income and no wealth is an obligation upon the son’s wealth. All of the scholars from whom we acquired knowledge are agreed that a man is obliged to spend on his children who have no wealth. 
Al-Mughni, 8/169, 170 
This spending which is a duty of the father is subject to certain conditions: the son should be in need of that money and be unable to earn himself either because he is too young or he is sick, etc., and the father should be able to afford it. 
Ibn Qudaamah (may Allah be pleased with him) said: 
For spending to be obligatory three conditions must be met: 
1 – they should be poor, with no wealth or income which makes them independent of means and able to do without others spending on them. If they have enough wealth or income to be independent of means, then there is no obligation to spend on them, because spending is for help, and the one who is independent of means does not need any help. 
2 – The one who is obliged to spend on them should have enough to spend on them, in addition to what he needs to spend on himself, either from his wealth or his income. If a person does not have any surplus, then he is not obliged to spend on them, because Jaabir narrated that the Messenger of Allah (peace and blessings of Allah be upon him) said: “If one of you is poor, let him start with himself; if he has any surplus wealth let him spend on his dependents, and if there is anything left after that let him spend on his relatives.” According to another version: “Start with yourself then with your dependents.” A saheeh hadeeth. And Abu Hurayrah narrated that a man came to the Prophet (peace and blessings of Allah be upon him) and said: “O Messenger of Allah, I have a dinar.” He said: “Spend it on yourself.” He said: “I have another.” He said: “Spend it on your child.” He said: “I have another.” He said: “Spend it on your wife.” He said: “I have another.” He said: “Spend it on your servant.” I said: “I have another.” He said, “You know best (on whom to spend it).” Narrated by Abu Dawood, 1691. Shaykh al-Albaani said: It is hasan in Sunan Abi Dawood. 
Because this is a kind of help, it is not obligatory for one who is in need, as is also the case with zakaah. 
3 – The who is spending should be an heir of the one on whom he is spending, because Allah says (interpretation of the meaning): 
“And on the (father’s) heir is incumbent the like of that (which was incumbent on the father)”
[al-Baqarah 2:233]
because the heirs are closely related, so the heir is more entitled to the money of the one from whom he would inherit than anyone else is, so the obligation of spending should apply to him in exclusion of all others. 
Al-Mughni, 8/168, 169 
So the father should spend on his son’s needs until he becomes independent of means. The scholars (may Allah have mercy on them) have stated that among the things on which a father is obliged to spend for his son is the expense of marriage if he needs to get married. 
Ibn Qudaamah (may Allah have mercy on him) said: 
Our companions said: The father must keep his son chaste if he is obliged to spend on him and if he needs help to remain chaste (by getting married). This is the view of some of the companions of al-Shaafa’i. 
Al-Mughni, 8/172 
Shaykh Saalih al-Fawzaan (may Allah preserve him) said: 
The son’s rights over his father come to an end when he becomes independent of means. When he grows up and starts to earn a living for himself, and is independent of means because of that earning, then his right of having his father spend on him comes to an end. But so long as he is still young, or he is grown up but is not yet independent of means and is unable to earn a living, then it remains his father’s duty to spend on him until he becomes independent of means. This is an obligation dictated by their close ties of kinship.  
Al-Muntaqa min Fataawa Shaykh al-Fawzaan, 3/240 
In conclusion: The father has to fear Allah with regard to those who have been entrusted to his care. If he is able to spend on his son’s education, medical care and other needs, then it is not permissible for him to fall short with regard to that. 
Our advice to you is that before you take this matter to court, you should ask good and righteous people to intervene and advise and exhort the father, and seek to bring about a reconciliation between him and his son. If he agrees to spend on his son willingly without getting the courts involved, that is better for the father’s peace of mind and will make him better disposed towards his son. 
Our advice to the son is to look for work which will make him independent of means so that he will not need to rely on his father – especially since the son has reached the age of manhood. He should try to combine work and study, which is a simple matter that has been done by many before him, for whoever seeks to become independent of means, Allah will help him. 
If he is unable to do that and the father persists in his attitude, then in that case there is nothing wrong with referring the matter to a sharee’ah judge (qaadi) to make the father do what he is obliged to do according to sharee’ah. But the more you are able to keep the matter away from courts and legal disputes, the better. 
And Allah knows best.