Is it permissible to dedicate the reward of fasting, praying (qiyam), and reciting the Quran in Ramadan to the soul of Prophet Muhammad (peace be upon him) and the soul of a deceased father?

It is not legislated to dedicate the reward of devotional acts to the Prophet, peace and blessings be upon him, for all the acts of obedience of the Ummah fall into his balance, as he is the one who guided to good.

As for dedicating the reward of fasting and prayer to a deceased father, if your intention is for yourself and you dedicate the reward to them, there is no evidence for its permissibility, even if some scholars have affirmed its validity.

Regarding dedicating the reward of reciting the Quran to the deceased, the preponderant view is that it reaches them. However, it is better for a Muslim to keep the reward of devotional acts for themselves to avoid scholarly differences, and to frequently supplicate for and invoke mercy upon the deceased Muslims.