Do acts of worship with specific functions—such as the prayer of repentance, supplications for protection, or Istikhara—not entail reward or good deeds, but rather their effect is limited to achieving their intended purpose only?

A person is rewarded for performing good deeds whenever they do so seeking the pleasure of Allah and out of obedience to Him and His Messenger. Allah Almighty has promised His servants immense rewards for all righteous deeds, among them His saying: (Whoever comes with a good deed will have better than it, and they will be safe from the terror of that Day) [An-Naml: 89], and His saying: (So whoever does an atom's weight of good will see it) [Az-Zalzalah: 7]. As long as the deed is for Allah, one is rewarded for it, even if it is from permissible matters like eating, drinking, and marital intimacy, if one intends thereby to gain strength for obeying Allah or to safeguard one's chastity, as the Messenger of Allah, peace and blessings be upon him, said: "And in the sexual act of one of you there is charity." A person is also rewarded for their permissible acts when they intend by them to seek assistance in obedience, as the Prophet, peace and blessings be upon him, said: "A man's expenditure on his family, which he reckons for Allah's sake, is charity."