Valmiki Ramayana Ayodhya Kanda Sarga 20 Shloka 15

नित्यम् always, व्रतपरायणा devoted to performing vows, सा she, क्षौमवसना clad in silk cloth, हृष्टा in delight, कृतमङ्गला having performed the rituals of auspiciousness, मन्त्रवत् in accordance with mantras, अग्निं fire, जुहोति स्म offered oblations.

Always engaged in the observance of vows, Kausalya (then) clad in silk cloth was performing rituals of auspiciousness, offering oblations to the firegod in accordance with mantras (Vedic hymns).