Verb
practice what one preaches (third-person singular simple present practices what one preaches, present participle practicing what one preaches, simple past and past participle practiced what one preached)
(American spelling) To act in harmony with one's teachings and advice.
That one should practice what one preaches is generally agreed, but anyone who has the indiscretion to preach what both he and his hearers practice must always incur-as Lord Chesterfield has incurred-the gravest moral reprobation. Logan Pearsall Smith