Is it permissible to save one-third of the salary designated for charity to use it as capital in a partnership with oneself on a fifty-fifty basis?

If the mentioned pledge is a vow (nadhr), such as saying, "It is incumbent upon me for the sake of Allah to give a third of my salary in charity," then it must be fulfilled, as the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him." In this case, one-third of the salary becomes a right of the poor, and it is not permissible to dispose of it otherwise. However, if the pledge was merely a thought and not uttered, then nothing is binding upon you, and you may dispose of it as you wish.