Professor Tom Egenes, in his book Introduction to Sanskrit: Part One lists vasudhaiva kuTumbakam as Manu Smirti 11.12.22.
Koenraad Elst wrote:
Dear list members,Does any of you know the references for two Sanskrit phrases which are very
routinely quoted nowadays:yatha pinde tatha brahmaande
and:
vasudhaiva kutumbakam
Yours sincerely,
Koenraad Elst