Sage Valmiki teaching Ramayana to Kusha and Lava is found in
the Bala Kanda chapter 1.4. This happened when Lord Rama was ruling the kingdom
of Ayodhya. Sage Valimiki composed the story of Ramayana in wonderful padas. He
recounted what had happened and what would transpire in the future.
Having composed the Ramayana, Sage Valmiki thought about who
would recount the tale. While he was thinking about this, Kusha and Lava came
and touched the feet of the sage. Mata Sita was residing in the ashram of Sage
Valmiki along with Kusha and Lava.
Sage Valmiki looked at the two brothers and knew they
possessed melodious voices. They looked like gandharvas – they possessed beauty
and auspicious signs. They knew about dharma and the intelligent ones were
accomplished in the Vedas.
Sage Valmiki then taught the Ramayana to Kusha and Lava. He
told them that the story is to be read and sung in pleasant tones, categorized
into three scales (high, low and accented) and seven notes
(sa-re-ga-ma-pa-dha-ni).
He told the two brothers that the song possesses rhythm that
can be adjusted to the tunes of stringed instruments. Ramayana is sung in nine
emotions – romance, comedy, compassion, ferocity, disgusting, horrible, heroic,
wonderful and peaceful.
Kusha and Lava possessed the knowledge of the gandharvas and
were accomplished in pausing and pitching their voices.
Having emerged from Rama’s body, they were like two mirror
images of him. Ramayana was a supreme account and devoted to dharma, the two
brothers learnt it in its entirety, reciting it in the proper way, without any
blemishes.
Controlled, and as instructed, the brothers sang this in
assemblies of sages, brahmanas and the virtuous.
Those who listened to the story had tears in their eyes and they
felt they had witnessed it in real.
On one occasion, while the brothers were singing on the
royal road of Ayodhya, Rama happened to hear them. He invited them to the
palace and asked them to recite the story of Ramayana.
Reference – The Valmiki Ramayana Volume I – Translated by
Bibek Debroy – Published by Penguin Books.