Let G be a reductive group over a local field F. Let O be the ring of integers of F.

The following are equivalent (and groups satisfying these conditions are called unramified):

(a) G is quasisplit and split after passing to an unramified extension of F.

(b) G is the generic fibre of a reductive group scheme over O.

This is stated, as far as I can tell without a proof or reference to one, in Tits' Corvallis article. My question is - how does one prove this equivalence?