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$\begingroup$Wait, do you want to allow for permutations, I mean, do you want to have also the combinations {x1,x2,x3} and {x2,x1,x3}? If so, then this might help Select[Permutations[Array[x, 10], 3], Length[#] == 3 &]$\endgroup$
Subsets[{x1, x2, x3, x4, x5, x6, x7, x8, x9, x10}, {3}]? $\endgroup${x1,x2,x3}and{x2,x1,x3}? If so, then this might helpSelect[Permutations[Array[x, 10], 3], Length[#] == 3 &]$\endgroup$