मनुस्मृति - गुरौ यत्र

गुरौ यत्र परीवादो निंदा वापि प्रवर्तते ।
कर्णौ तत्र पिधातव्यौ गंतव्यं वा ततोऽन्यतः ॥

- मनुस्मृति

If one finds irresponsible people slandering his teacher, he must immediately close his ears. It is better if he moves away from such a place. This is important because listening to such slander will cause doubt in one's mind regarding his master. He will not be able to follow the teacher completely if such doubt exists.

- Manu Smriti