Responsa על חולין 209:60

Q. We have heard that you refrain from eating meat after cheese for the same interval as cheese after meat, and that you do eat poultry-meat after cheese. Is this report true?
A. Yes, one may conduct oneself more strictly than required by the Law in order to make sure that one be not exposed to sin, without being guilty of the sin of adding anything to the Law.
R. Meir adds that in his youth he used to scoff at those persons who were so meticulous. He even considered their practice heretical, until he once found small particles of cheese between his teeth hours after he ate it. He, therefore, decided to be more careful.
SOURCES: Pr. 615; L. 500; Mord., Hulin, 68; cf. Tashbetz, 355.

Q. We have heard that you refrain from eating meat after cheese for the same interval as cheese after meat, and that you do eat poultry-meat after cheese. Is this report true?
A. Yes, one may conduct oneself more strictly than required by the Law in order to make sure that one be not exposed to sin, without being guilty of the sin of adding anything to the Law.
R. Meir adds that in his youth he used to scoff at those persons who were so meticulous. He even considered their practice heretical, until he once found small particles of cheese between his teeth hours after he ate it. He, therefore, decided to be more careful.
SOURCES: Pr. 615; L. 500; Mord., Hulin, 68; cf. Tashbetz, 355.