Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 7 · Samskara Muhurtas
संस्कारमुहूर्ताः
बालस्य बलहीनोऽपि सितो जीवः शुभप्रदः ।यथोक्तवत्सरे कार्यमनुक्ते नोपनायनम् ॥ ३५० ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 350.
For the boy, Venus and Jupiter give good results even when weak. Do the thread rite in the year as told. Where no year is told, it is not done.
Simple meaning: Venus and Jupiter help a boy even when weak. Keep to the years given for the rite.
दृश्यमानगुरौ शुक्रे शाखेशे चोत्तरायणे ।
Do the thread rite when Jupiter, Venus and the lord of one's Veda are visible, in the Sun's northward course.
शरद्ग्रीष्मवसंतेषु व्युत्क्रमात्तु द्विजन्मनाम् ।
Autumn, summer and spring, in reverse order for the three twice-born groups, are best. Five months from Magha are ordinary.
स्वकुलाचारधर्मज्ञो माघमासे तु फाल्गुने ।
A thread rite in Magha brings family knowledge, in Phalguna knowledge of rules, in Chaitra wealth and learning.