Which is more greatly rewarded by God: waiving the payment for volunteer work for the organization itself, or receiving it and then donating it with the donor’s knowledge?

The most beneficial act for people is the dearest act to Allah and the greatest in reward; as the Prophet, peace and blessings be upon him, said: "The most beloved of people to Allah Almighty are those most beneficial to people, and the most beloved of deeds to Allah Almighty are: a joy you bring to a Muslim, or relieving him of a hardship, or paying off a debt for him, or driving away his hunger." So, the best is what is most beneficial to Islam and Muslims, whether by earning a wage and giving it in charity or through voluntary work.