A good disciple does not violate any Guru's instruction even mentally

गुरुमाहात्म्यं नाम पञ्चदशोऽध्यायः

Guru's importance Chapter 15

उपमन्युरुवाच |

Upamanyu said (to Lord Krishna)

श्रेयोऽर्थी यदि गुर्वाज्ञां मनसापि न लंघयेत् |
गुर्वाज्ञापालको यस्माज्ज्ञानसंपत्तिमश्नुते || 23 ||

If a good disciple does not violate any Guru's instruction even mentally, from that the follower of Guru's instructions (he) obtains knowledge and prosperity.