Your search for "Those that vow the most are the least sincere. - Richard Sheridan 1751 - 1816" revealed the following:

Those that vow the most are the least sincere. - Richard Sheridan 1751 - 1816 - RW-23.3

Those that vow the most are the least sincere. - Richard Sheridan 1751 - 1816 - Drink Wisely in MugWisdom - Ceramic 11oz cup