“And the truly dear or ultimate principle of friendship is not for the sake of any other or further dear.”
Socrates examines whether some cherished thing can be valued for its own sake rather than only because it leads to another benefit. He advances a possible ultimate object of friendship, but the argument immediately faces further questions and the dialogue finishes without an agreed definition. Reading this as a tested hypothesis prevents the line from becoming a misleading slogan about ideal friendship.
Source details
Plato, Lysis, approximately 219c–d, Socrates speaking with Lysis and Menexenus; Benjamin Jowett English, Project Gutenberg #1579. The sentence follows a chain of examples of things desired for other things, and Socrates soon reopens the argument by asking whether friendship depends on evil. It is a provisional dialectical step, not a conclusive formula offered by Plato.