What is the correct part of the phrase: "What cannot be wholly attained should not be entirely abandoned..."?

This saying is a sound principle and profound wisdom, not a hadith (definition), as mentioned by Al-Ajlouni and others. It has been reported in various forms such as: "What cannot be achieved in its entirety should not be abandoned in its entirety," or "its most should not be abandoned." Its equivalent in revelation is the Almighty's saying: "So fear Allah as much as you are able," and the Prophet's (peace and blessings be upon him) saying: "And what I have commanded you, do of it as much as you are able."