What is the reference for Abdullah ibn al-Mubarak's action of spending his money on the poor and not completing his supererogatory Hajj, and is it better to donate all the funds allocated for a supererogatory Hajj than to complete it?

Originally, Hajj and Umrah are superior to voluntary charity, as they encompass spending and other acts of worship. However, if special circumstances arise, such as needy relatives or people in distress, and it is impossible to combine the two, then spending (charity) is better in this situation, as reported from Imam Malik and Ibn Taymiyyah. An example of this is the story of Abdullah ibn al-Mubarak, who turned back from his Hajj to provide money to a distressed family.