Anguttara Nikaya I. 188
As they sat there, the Kalamas of Kesaputta said to the Blessed One, "Lord, there are some priests and contemplatives who come to Kesaputta. They expound and glorify their own doctrines, but as for the doctrines of others, they deprecate them, revile them, show contempt for them, and disparage them. And then other priests and contemplatives come to Kesaputta [and do the same]. They leave us absolutely uncertain and in doubt: Which of these venerable priests and contemplatives are speaking the truth, and which ones are lying?" "Of course you are uncertain, Kalamas. So in this case, Kalamas, don't go by reports, by legends, by traditions, by scripture, by logical conjecture, by inference, by analogies, by agreement through pondering views, by probability, or by the thought, 'This contemplative is our teacher.' When you know for yourselves that, 'These qualities are unskillful; these qualities are blameworthy; these qualities are criticized by the wise; these qualities, when adopted and carried out, lead to harm and to suffering'—then you should abandon them.