Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 7 · Samskara Muhurtas
संस्कारमुहूर्ताः
कर्तव्यं क्षौरनक्षत्रेऽप्यथ वास्योदये शुभम् ।नृपविप्राज्ञया यज्ञे मरणे बन्धमोक्षणे ॥ ३४२ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 342.
It should be done on a shaving star, or else with a good lagna (rising sign) for it. It may also be done on the order of a king or a Brahmin. So too at a sacrifice, at a death and at a release from prison.
Simple meaning: Shave on a good star or lagna. It is also allowed at a king's order, a sacrifice or a death.
उद्वाहेऽखिलवारर्क्षतिथिषु क्षौरमिष्टदम् ।
At a wedding shaving is allowed on any day. In lucky rites the razor is offered first.
नवमे सप्तमे वापि पञ्चमे दिवसेऽपि वा ।
Choose the 9th, 7th, 5th or 3rd day before the rite, a good star, weekday and lagna.
आधानादष्टमे वर्षे जन्मतो वाग्रजन्मनाम् ।
The sacred thread is tied in the 8th year for Brahmins, the 11th for kings and the 12th for Vaishyas.