In 1986 the crew of Soyuz T15 performed a unique mission where they visited 2 space stations and helped move important gear from the old station to the new one. Salyut7 had unifinished business, Mir was the new hotness, and the crew were able to visit both as part of an extended mission.

References and further reading:
Mir Hardware Heritage David S Portree
https://spaceflight.nasa.gov/history/...

Russian Space Web Anatoly Zak
http://russianspaceweb.com/