Circumstances alter cases

Circumstances alter cases.

Prov. In unusual situations, people are allowed to do unusual things. Cashier: I'm sorry, this store does not accept personal checks. Customer: But I need this medicine, and I don't have any cash. I've shopped at this store for fifteen years. Surely you can trust me this once. Cashier: Well, all right. Circumstances alter cases.
See also: alter, case, Circumstance
References in classic literature ?
I own I've set my face against it hitherto, but circumstances alter cases.
Circumstances alter cases as the history of WW2 demonstrates.
Circumstances alter cases, and I do not hold the view that all councillors who claim these expenses are necessarily only in it for themselves.
I know that times change, and that circumstances alter cases, but this strikes me as the weirdest U-turn of all time.