[vivegi]

Time, Clocks and the Ordering of Events in a Distributed System. Communications of the ACM 21, 7 (July 1978), 558-565. Reprinted in several collections, including Distributed Computing: Concepts and Implementations, McEntire et al., ed. IEEE Press, 1984. PDF https://lamport.azurewebsites.net/pubs/time-clocks.pdf

Lamport cites

> The origin of this paper was the note The Maintenance of Duplicate Databases by Paul Johnson and Bob Thomas. I believe their note introduced the idea of using message timestamps in a distributed algorithm. I happen to have a solid, visceral understanding of special relativity (see [5]). This enabled me to grasp immediately the essence of what they were trying to do.

The Maintenance of Duplicate Databases, Paul Johnson and Bob Thomas (1975). https://www.rfc-archive.org/getrfc.php?rfc=677

Leslie Lamport's website link to Time Clocks. https://lamport.azurewebsites.net/pubs/pubs.html#time-clocks