Is one obligated to adhere to the Fast of David (peace be upon him) for life, or is it prescribed for a limited period?

Continuing to observe the fast of Dawud (peace be upon him) is the best and most beloved voluntary fast, but it is not obligatory except by vow. A condition for the virtue of this fast is that it should not weaken the body from fulfilling the obligatory rights of Allah and the rights of people. If the fast weakens one from doing so, then abandoning it is better. It is not a condition for receiving the reward of fasting that one performs it throughout their entire life; whatever one does, they will be rewarded for it if it meets the conditions for the acceptance of righteous deeds. It is disliked for a Muslim to commit to a supererogatory act that they know they will be unable to sustain, due to the rejection this entails of the guidance of ease in religion and the fear of falling short in obligations. For this reason, it was said regarding Dawud: "And he does not flee when he meets [the enemy]."