Exceptio probat regulam
Defined in 2 dictionaries — Ballentine's (1916), Black's (1910)
Ballentine's Law Dictionary
James A. Ballentine · 1916
The exception proves the rule. See 101 Me. 581, 8 L. R. A. (N. S.) 104, 64 Atl. 1048.
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
The exception proves the rule. 11 Coke, 41; 3 Term, 722. Sometimes quoted with the addition "de rebus non exceptis," ("so far as concerns the matters not excepted.")