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