Source: Taittiriya Upanishad, Shikshavalli I.11.2

मातृदेवो भव। पितृदेवो भव।
आचार्यदेवो भव। अतिथिदेवो भव।
यान्यनवद्यानि कर्माणि तानि सेवितव्यानि। नो इतराणि।
यान्यस्माकँ सुचरितानि तानि त्वयोपास्यानि। नो इतराणि॥

mātṛdevo bhava। pitṛdevo bhava।
ācāryadevo bhava। atithidevo bhava।
yānyanavadyāni karmāṇi tāni sevitavyāni। no itarāṇi।
yānyasmākam̐ sucaritāni tāni tvayopāsyāni। no itarāṇi॥

माता को, पिता को, आचार्य को और अतिथि को देवता के समान मानकर उनके साथ व्यवहार करो।
जो भी कार्य अहंकार से मुक्त होते हैं, उनका अनुसरण करना चाहिए, दूसरों का नहीं।
हमारे (शिक्षकों के) बीच जो भी अच्छा आचरण करते हैं, केवल उसी का अनुसरण करो, दूसरों का नहीं।

Be one to whom a mother is as a god, be one to whom a father is as a god,
Be one to whom an Acharya (spiritual guide, scholars you learn from) is as a god, be one to whom a guest is as a god.
Whatever actions are free from egoism, they should be practiced, not others.
Whatever good conduct you find among us (teachers), that alone should be practiced, not others.