先例

Don't take this as a precedent.

There is no precedent to it.

There is no lack of precedents (in this connection).

according to a historical precedent

have precedents to go by

have no precedent to go by

follow a precedent

quote/follow a precedent

copy the precedent

violate a precedent

give/serve as precedent (for sth)

create/establish/set a precedent

break (with) a precedent