Bartlett's Familiar Quotations is one of the classic gold standards. It's reasonably well-sourced, and it separates out "attributed" but uncomfirmed remarks. It

Bartlett's Familiar Quotations is one of the classic gold standards. It's reasonably well-sourced, and it separates out "attributed" but uncomfirmed remarks. It's not as comprehensive as the online sites, since it's edited as a physical book, but it's pretty reliable: https://en.wikipedia.org/wiki/Bartlett%27s_Familiar_Quotations https://en.wikipedia.org/wiki/Bartlett%27s_Familiar_Quotatio... It's an American work, so I don't have a good sense for how well it covers other regions' quotations.