noun
Refers to a past case or instance that serves as a reference, often in negative constructions like ためしがない (there is no precedent / it has never happened).
こんなに早く雪が降ったためしはない。
There is no precedent for snow falling this early.
彼が約束を守ったためしがない。
He has never kept a promise.
れい is the common reading for 'example' in general contexts; ためし is more limited and often used in set phrases about precedents or past occurrences.
The reading ためし is a native Japanese word (kun'yomi) attached to the kanji 例, which carries the meaning of 'example' or 'precedent'.