Skandapurana 1.4.38.53

1.4.38.53

gaṃgodakumbhaḥ syādyadvattanmadhye madyabiṃdunā..
aśivajñasya yo bhuṃkte śivajño'pi tathaiva saḥ.. 40.53 ..

Just as a pot of Gaṅgā water becomes [polluted] by a drop of liquor within it, / so is he who eats [food] from one who knows not Śiva, even though he himself knows Śiva.'"