Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 7 · Samskara Muhurtas
संस्कारमुहूर्ताः
उपवीती युग्मतिथावनग्नः कामयेत्स्त्रियम् ।पुत्रार्थी पुरुषस्त्यक्त्वा पौष्णमूलाहिपित्र्यभम् ॥ ३१९ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 319.
A man who wants a son should go to his wife on an even tithi (moon day). He should wear the sacred thread and not be naked. He should leave out Revati, Mula, Ashlesha and Magha.
Simple meaning: A man who wants a son should keep to even moon days and avoid four stars.
प्रसिद्धे प्रथमे गर्भे तृतीये वा द्वितीयके ।
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.