Rashi on Numbers 19:4/רש"י על במדבר י״ט:ד׳

1אל נכח פני אהל מועד [HE SHALL SPRINKLE THE BLOOD] TOWARDS THE FRONT SIDE OF THE APPOINTED TENT He stands at the East of Jerusalem and must direct his gaze straight towards the entrance of the Hechal at the time of sprinkling the blood (Sifrei Bamidbar 123:2; Yoma 68a).