I was wondering could anyone tell me a reference for the fact that an absolutely quasi-simple algebraic group over a non-archimedean local field which is centreless and non-compact acts faithfully and Weyl transitively on a regular locally finite building, and its image in the automorphism group is closed in the compact-open topology? 



algebraic groups over non-archimedean local fields acting on buildings
For such a general assertion, independent of classification, you'd need some one of the F. Bruhat and J. Tits papers, but (since I do not have copies nearby) I could not point you to any precise location within them. 


F. Bruhat and J. Tits, BN-paires de type affine et donnees radicielles, C.R. Acad. Sci. Paris serie A, vol 263 (1966), pp. 598-601.


F. Bruhat and J. Tits, Groupes simples residuellement deployes sur un corps local, ibid, pp. 766-768.


F. Bruhat and J. Tits, Groupes algebriques simples sur un corps local, ibid, pp. 822-825.


F. Bruhat and J. Tits, Groupes algebriques simple sur un corps local: cohomologie galoisienne, decomposition d'Iwasawa et de Cartan, ibid, pp. 867-869.


F. Bruhat and J. Tits, Groupes Reductifs sur un Corps Local, I: Donnees radicielles valuees, Publ. Math. I.H.E.S. 41 (1972), pp. 5-252.


F. Bruhat and J. Tits, Groupes Reductifs sur un Corps Local, II: Schemas en groups, existence d'une donnee radicielle valuee, ibid 60 (1984), pp. 5-184.


F. Bruhat and J. Tits, Schemas en groupes et immeubles des groupes classiques sur un corps local, Bull. Soc. Math. Fr. 112 (1984), pp. 259-301.


F. Bruhat and J. Tits, Groupes Reductifs sur un Corps Local, III: Complements et applications a la cohomologie galoisienne, J. Fac. Sci. Univ. Tokyo 34 (1987), pp. 671-688. 


