Musnad Abu Ya'la al-Mawsili 233:1

My father sought permission from the Prophet, may Allah bless him and grant him peace, and he entered between him and his shirt from behind him. He began to embrace him, then he began to say, "O Prophet of Allah, what is the thing that is not permitted to be withheld?" He said, "Water." He said, "O Prophet of Allah, what is the thing that is not permitted to be withheld?" He said, "Salt." He said, "O Prophet of Allah, what is the thing that is not permitted to be withheld?" He said, "That you do good is better for you." He said, so he stopped at water and salt. He said, and that man would not withhold anything of water, even if it were little.