Valmiki Ramayana Ayodhya Kanda Sarga 20 Shloka 14
Original Shlokaकौशल्यापि तदा देवी रात्रिं स्थित्वा समाहिता। प्रभाते त्वकरोत्पूजां विष्णोः पुत्रहितैषिणी।।2.20.14।।
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तदा then, कौशल्या Kausalya, रात्रिम् night, समाहिता with composed mind, स्थित्वा remaining (in meditation), प्रभाते in the early morning, पुत्रहितैषिणी to secure her son's welfare, विष्णोः Visnu's, पूजाम् worship, अकरोत् performed.
Having spent the night with a composed mind (abosorbed in meditation), Kausalya was worshipping lord Visnu in the early morning to secure her son's welfare.