Devibhagavatapurana 7.36.26

7.36.26

tasmācchāstrasya siddhānto brahmadātā guruḥ paraḥ |
śive ruṣṭe gurustrātā gurau ruṣṭe na śaṅkaraḥ ||

In all the Siddhântas (decided conclusions) of the S'âstras, it is stated that the Guru who imparts the knowledge of Brahman is the best and the most honourable. If S'iva, becomes angry, the Guru can save; but when the Guru becomes angry, S'ankara cannot save. So the Guru should be served with the utmost care.