Does regret over giving charity to an unintended person affect its reward, given the intention to give it for the sake of Allah and for healing?

Regret over not giving charity to a specific person does not prevent its reward, because the regret is not over the righteous deed itself, and this does not invalidate the reward. The Sunnah has indicated this, as in the Hadith of Yazid Al-Sulami, his charity was accepted even though he did not intend for his son to be the recipient of the charity. Similarly, in the Hadith of Abu Hurayrah concerning the man who gave charity to a prostitute, a rich person, and a thief, his charity was accepted and he attained its reward, because his intention was righteous, even if the charity did not go to the place he initially intended. This indicates that the righteous intention of the giver of charity is the basis for its acceptance.