Ruth 1:16 says: And Ruth said, Intreat me not to leave thee, or to return from following after thee: for whither thou goest, I will go; and where thou lodgest, I will lodge: thy people shall be my people, and thy God my God:
(KJV).
The verse is spoken by Ruth to her mother-in-law Naomi in Ruth 1, after the death of Ruth's husband. Read it in context at Ruth 1:16, or the full chapter at Ruth 1.