https://quoteinvestigator.com/2019/07/30/lawyer/
He who will take no-Advice, but be always his own Counsellor, shall be sure to have a Fool for his Client.
Alternatively there is this
https://www.quora.com/What-does-the-phrase-a-man-who-is-his-own-lawyer-has-a-fool-for-a-client-mean#:~:text=The phrase "a man who,can lead to unfavorable outcomes.
The phrase "a man who is his own lawyer has a fool for a client" is a time-honored adage emphasizing the risks of representing oneself in legal matters. Essentially, it suggests that taking on the role of your own lawyer, rather than hiring a professional, is unwise and can lead to unfavorable outcomes.