Using find would be one way.  For example, to find (print) all files in the file system that have been modified/created in the last three days:

$ find / -mtime -2
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Update: actually, rereading your question I see you wrote file (singular), whereas I had read files ...  So, to get the one most recent file only, it would rather be something like

$ find / -mtime -2 -type f -exec ls -l {} \; | sort -k6 | tail -1
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