Sir Isaac Newton, Roger Cotes (1850). “Correspondence of Sir Isaac Newton and Professor Cotes: Including Letters of Other Eminent Men Now First Published from the Originals in the Library of Trinity College, Cambridge; Together with an Appendix, Containing Other Unpublished Letters and Papers by Newton; with Notes, Synoptical View of the Philosopher's Life, and a Variety of Details Illustrative of His History”, p.284
Cosmos ch. 1 (1980). Sagan denied using the phrase "billions and billions," as caricatured by comedian Johnny Carson, but the above quote approaches that phrase, and Sagan was extremely fond in his writing of the word billion or billions.