Constitution of Bangladesh
PART III - FUNDAMENTAL RIGHTS
35. (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 or different from that which might have been inflicted under the law in force at the time of the commission of the offence.
Nullum crimen sine lege
Nulla poena sine lege
EDIT.