Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 38

Sanskrit:

सा तत्पुंसवनं राज्ञी प्राश्य वै पत्युरादधे ।गर्भं काल उपावृत्ते कुमारं सुषुवेऽप्रजा ॥ ३८ ॥

ITRANS:

sā tat puṁ-savanaṁ rājñīprāśya vai patyur ādadhegarbhaṁ kāla upāvṛttekumāraṁ suṣuve ’prajā

Translation:

Although the Queen had no son, after eating that food, which had the power to produce a male child, she became pregnant by her husband, and in due course of time she gave birth to a son.

Purport:

Among the ten kinds of purificatory processes, one is puṁ-savanam, in which the wife is offered some prasāda, or remnants of foodstuff offered to Lord Viṣṇu, so that after sexual intercourse with her husband she may conceive a child.