Shaikh Uthaimeen, may Allaah have mercy on him, said,

“Giving precedence to others over yourself in those things which are obligatory is not allowed. For example, if a person only has enough water for himself with which to perform ablution and there is another person with him who needs water, he is not to give the water to the other person, the other person should do tayammum.  Because this is giving precedence to others over yourself in those things which are obligatory, and giving such precedence to others over yourself is haraam.’

Ash-Sharh al-Mumti’, vol. 15, p. 40.