I'm not sure this is actually a "trope", as such. Any group of people travelling to accomplish a task could be considered examples of this "trope", even IRL groups such as a squad of soldiers. That doesn't mean they were influenced by earlier depictions.

In gaming, this is certainly a trope with a specific origin - we can trace it's lineage pretty clearly from D&D - but that origin was perhaps more influenced by practical concerns than by fictional or historical accounts. In the fiction that early D&D drew on, groups were either smaller (late LOTR has a "party" of 2-3 depending on whether you count Gollum as a hero or not; the Fafhrd and the Gray Mouser stories similarly focus on a duo of close friends), larger (The Hobbit has 13 dwarves!), or no "party" at all and just a solo hero. Early D&D had similarly chaotic party sizes, with sometimes over 20 players at once crowding in Gygax's basement with 1-2 DMs between them, some of whom would be playing multiple characters with retainers and so on. D&D eventually converged on the "classic party" of 3-7 players and one DM because they found that that's what produces the most fun, rather than in explicit imitation of literary models.

With all that said, we might look at some well-known classic examples of "adventuring parties".

Jason and the Argonauts are a decent example. Travelling from island to island on a long-term quest (acquire the Golden Fleece), with shorter adventures at each stop along the way, this collection of colourful characters is in many ways very similar to a D&D party (although, like the Knights of the Round table, more numerous - up to 85 in some versions, although of course they frequently lost or gained members.) This story or collection of stories evolved over time, but is already in it's archetypal form in the early 3rd century BC in Apollonius of Rhodes' epic Argonautica.

Journey to the West, written in China in the 16th century AD but based very loosely on the life of Xuanzang in the 7th century AD, could be considered an example. In the story, Xuanzang collects four fantastical disciples, who travel and have adventures along with him across various imaginary lands.

One could even argue the Epic of Gilgamesh, the earliest surviving story c. 1900 BC, is an example of this trope. A chunk of the story is devoted to two heroes Gilgamesh and Enkidu wandering around having adventures, much like a fantasy adventuring party.