Perhaps you're thinking of a sentence with:
* Three verbs ending in -ed: This is possible but not a specific grammatical rule. For example, "The dog was chased, caught, and fed by the farmer."
* Three words ending in -ed: This is also possible but not a rule. For example, "The tired, worried, and stressed student finally finished their essay."
It's important to remember that English grammar focuses on the meaning and function of words within a sentence, rather than specific letter combinations.