Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 7 · Samskara Muhurtas
संस्कारमुहूर्ताः
प्रसिद्धे प्रथमे गर्भे तृतीये वा द्वितीयके ।मासे पुंसवनं कार्यं सीमंतं च यथा तथा ॥ ३२० ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 320.
When the first pregnancy is clear, do pumsavana (rite for a son) in the 2nd or the 3rd month. Do simantonnayana (hair-parting rite) in the same way.
Simple meaning: The rite for a son is done in the 2nd or 3rd month of the first pregnancy.
चतुर्थे मासि षष्ठे वाप्यष्टमे वा तदीश्वरे ।
Choose the 4th, 6th or 8th month, when the Moon and the stars suit both parents.
अरिक्तापर्वदिवसे कुजजीवार्कवासरे ।
Pick a day with no empty or junction tithi, on Tuesday, Thursday or Sunday, with the Moon in a male navamsha.
शुद्धेऽष्टमे जन्मलग्नात्तयोर्लग्ने न नैधने ।
Keep the 8th house clean, avoid the 8th from either parent's birth lagna, and let good planets support the rising sign.