Protection from Ex post facto laws is covered under which Article of the Constitution?

Ex post facto law is derived from the Latin word “ex post facto” which means ‘out of the aftermath’, it is a law that has a retrospective consequence on any act committed, which is not prohibited by law, before the enactment of a preceding law. Art. 20 (1) provides protection to the accused from ex post facto laws. Art. 20. Protection in respect of conviction for offences .—(1) No person  shall be convicted of any offence except for violation of a law in force at the  time of the commission of the Act charged as an offence, nor be subjected to a  penalty greater than that which might have been inflicted under the law in force  at the time of the commission of the offence.