Well I just "had" to look it up, but couldn't find the exact Canon I ran across recently. (the indexes aren't much help sometimes) But I did find this Canon, which is not the exact Canon I was thinking of.
Anyways, here's the whole thing:
Whenever a Bishop goes from one city to another city, or from one province to another province, for the sake of vaunt with a view to having eulogies bestowed upon him, or to appearing to be devoted to the religion, and desires to stay there too long a time, and the Bishop of that city is not an experienced teacher, we decree that he shall not treat the latter scornfully, and deliver sermons too continuously, and thereby endeavor to bring disgrace and ignominy upon the Bishop of that place. For this excuse has been wont to cause trouble, and such cunning rascality shows that he is endeavoring to court and to usurp the other’s benefice, and will not hesitate to abandon the church assigned to him and to step over into the other one. The time, therefore, for this must be fixed (since it has been deemed to be nothing short of inhuman and rude not to welcome a visiting Bishop]. Remember that in time past our fathers judged that if any layman staying in a city three Sundays should fail to attend church for three weeks in succession, he should be denied communion. If, therefore, this has been made a law as respects laymen, no Bishop must or ought or can without disadvantage stay away from his own church for any great length of time, and grieve the laity entrusted to him, unless he be under some grave necessity or in some difficult situation. - The 11th Canon of the Council of Sardica
I have several copies of the Canons, including The Rudder, which all has footnotes and references to other Canons that refer to same subject but there's a bunch of them. This is the basic idea though, though it's technically not the one I ran across the other day.