Skandapurana 5.73.33

5.73.33

yadatra kriyate kiṃcitkarma dharmyaṃ dvijottamāḥ ..
tadbāhyaṃ ca bhavedvyarthametadvidmaḥ sphuṭaṃ vayam .. .. 33 ..

Whatever religious act is performed here, O best of the twice-born,
if done by an outsider, becomes useless—this we clearly know.