Praise be to Allah.
It should be understood that the basic principle is that the sick person should not be forced to consume any food or drink that he does not want, because of the report narrated by at-Tirmidhi (2040) and Ibn Maajah (3444) from ‘Uqbah ibn ‘Aamir al-Juhani who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Do not force your sick ones to eat or drink. Allah will feed them and give them to drink.”
Abu ‘Eesa said: This hadith is hasan ghareeb; we only know of it from this isnaad. Al-Albaani said: It is saheeh.
It says in the commentary on Sunan Ibn Maajah by as-Suyooti and others (1/246): “Do not force your sick ones” means: if they do not eat willingly, and do not say: He is growing weak because of lack of food, “for Allah, may He be blessed and exalted, will feed them and give them to drink” i.e., He will grant them patience and strength, for patience and strength truly come from Allah, not from food and drink, and not because of one’s good health. Al-Qaadi said: That is, He will nourish them and preserve their physical well-being in a similar way to that in which food and drink may benefit one by preserving life and giving physical well-being.
How many benefits there are in this Prophetic advice, and it is worthy of doctors paying attention to it, because if the patient does not feel like eating or drinking, that is because his body is preoccupied with resisting the sickness, so giving him food in this situation may be very harmful, as the Prophet (blessings and peace of Allah be upon him) said: “Allah will feed them and give them to drink” that is, without them consuming food and drink. End quote.
Ibn al-Qayyim (may Allah have mercy on him) said in Zaad al-Ma‘aad fi Hadiy Khayr al-‘Ibaad (4/83):
Some prominent doctors said: what great benefit this prophetic advice contains, because it is based on divine wisdom, especially for doctors and those who treat the sick. That is because if the patient does not feel like eating or drinking, it is because his body is preoccupied with fighting the sickness, or because his appetite is not there, or it is weak because his internal heat is weak or very low. Whatever the case, it is not permissible to give him food in that case, when he is in that condition.
It should be noted that hunger is the result of different parts of the body seeking nourishment, because nature seeks to replace what is used up of them. So the furthest parts of the body are pulled towards the closer parts, until that pulling reaches the stomach, whereupon the individual feels hungry and will therefore seek food. But when there is sickness in the body, the body will naturally be preoccupied with dealing with its cause, fighting it and expelling it, and will not be interested in seeking food or drink. But if the patient is forced to eat or drink, then the natural defences of the body will stop working and will begin to focus on digesting the food and distributing nutrients, and it will not be able to focus on fighting the substance that caused the sickness and warding it off. Thus that will be the cause of harm to the patient. End quote.
Modern medicine has proven that there are a great deal of stored sources of nourishment in the body which the body can use at times when it is deprived of food, and most sickness is accompanied by loss of appetite in the patient; force-feeding in this situation will be harmful to him, because his digestive system is not going to be functioning as it should, which will lead to difficulty in digestion and the patient will get worse. You can see more information on the following link:
Therefore it is not permissible to force the patient to eat and drink, unless he has reached the point where it is feared that he will die if he does not consume any food. In that case it is permissible to give him food, as appropriate to his situation, and this is a matter to be determined by specialist doctors.
As for forcing the patient to take medicine, the basic principle is that this is not recommended. This was stated by the Shaafa‘i fuqaha’. An-Nawawi (may Allah have mercy on him) said in al-Majmoo‘ Sharh al-Muhadhdhab (5/118):
it is recommended not to force the patient to take medicine or consume other food. End quote.
But if there is the fear that the patient may die if he does not take the medicine, then what appears to be the case – and Allah knows best – is that in this situation he may be forced to do that. It says in ad-Durar al-Bahiyyah fi Sharh al-Bahjah al-Wardiyyah (2/78):
It says in ar-Rawdah: It is makrooh to force him to take medicine. End quote.
What appears to be the case that this applies in cases where it is not known or it is thought that not taking the medicine may lead to death. End quote.
Based on the words of the fuqaha’ (may Allah have mercy on them) quoted above, it seems that what you did by allowing the doctors or nurses to give your father (may Allah have mercy on him) food and medicine by force, only came about after you feared that he would die or that his sickness would get worse if he did not take his medicine or eat any food. There is no blame on you for this, in sha Allah, and it is not regarded as disobedience towards your father. Rather it was kindness towards your father. So do not open the door to insinuating thoughts and grief because of that.
It should be noted that part of kindness towards your father after his death includes offering a lot of supplication for him, asking for mercy for him, and praying for forgiveness for him, and giving charity on his behalf. These are things that may benefit the deceased, by Allah’s leave, as we have explained in fatwa no. 42384.
And Allah knows best.