Story of Skanda as contained in Valmiki Ramayana
From Translation of Valmiki Ramayana
Today is Skanda Sashti and many of you may be wondering , which is the first book , which tells about the stiry of Skanda
I am sure many of you do not know that Sage Viswamithra told the story Of Skanda, possibly for the first time in our epics to Sri Rama and his brother Lakshmana (Chapters 35, 36, 37 of Bala Kanda .Those interested to know the full story may read my translation https://englishvalmikiramayanam.blogspot.com/2013/06/bala-kanda-27-49.html
You may also be interested to know that the famous sloka of Waking up Rama “kausalya Supraja Rama,,,” is the first sloka of chapter 35 . The story told in these chapters is slightly different from the story of Lord Subrahmanya that we all know)
Summary of the story contained in these chapters of Ramayana
Rama along with the sages reach the banks of river Ganges and they stay there for a night. When Rama asks about the river Ganges, Viswamithra starts telling him about the river. He tells them she was the first daughter of “ Himalayas and Mena” and as per the request of devas, she becomes a river and is taken to deva loka.
Her sister Uma does penance and marries Lord Shiva Shiva and Uma lead a family life but no children are born to them. Worried that all the three worlds would be destroyed if a son to both of them is not born to them , at the request of devas, the earth receives the seed of Shiva , which flowers in to a God within fire. That God is Karthikeya. Uma curses the devas as well as earth and Shiva and Uma do further penance.
The devas who needed a commander to their army approached Brahma and he asked them to make the seed of Shiva which was with fire God to be placed in the wombs of Ganga. Since she was not able to tolerate his heat, he was slid down on the rivers and for suckling him the Krithika maidens are appointed. He develops six faces to drink milks from six maidens. He grows up in a day and is anointed as their commander by the devas.
Saying this sage Viswamithra says
“Oh Rama, Now I have told you in great detail the story of Ganga and also told you about the birth of the divine and honored lad.” 37.31
“Oh Rama the devotees among human beings of earth of this Karthikeya would live long, have sons and grandsons and in the end would go to the world of Skanda.”