Floyd's Assigning Meaning to Programs (1967), https://people.eecs.berkeley.edu/~necula/Papers/FloydMeaning.pdf, came out two years before Hoare's An Axiomatic Basis for Computer Programming (1969), https://dl.acm.org/doi/10.1145/363235.363259. He had the same basic idea and applies it to two examples: a flowchart language and an ALGOL subset. He even uses the term "strongest verifiable proposition" in a way very reminiscent of Dijkstra's later "strongest postcondition/weakest precondition".
