Mbh 13.86.2a

"'Bhishma said, "The gods and the Rishis, O monarch, reduced to great distress (by Taraka's prowess and the conduct of Ganga in casting off Agni's seed), urged the six Krittikas to rear that child. Amongst the celestial ladies there were none, save these, that could, by their energy, bear the seed of Agni in their wombs. The god of fire became exceedingly gratified with those goddesses for their readiness to sustain the conception caused by the cast off seed of Agni which was endued with his own high energy. When the energy of Agni, O king, was divided into six portions and placed within the channels (leading to the womb), the six Krittikas began to nourish the portion that each held in her womb. As the high-souled Kumara, however, began to grow within their wombs, their bodies being afflicted by his energy, they failed to obtain peace anywhere (in heaven or on earth). Filled with energy as their bodies were, the time at last came for delivery. All of them, it so happened, O prince of men, delivered at the same time. Though held in six different wombs, yet all the portions, as they came out, united into one. The goddess Earth held the child, taking it up from a heap of gold. Verily, the child, endued with excellent form, blazed with splendour even like the god of Fire. Of beautiful features, he began to grow in a delightful forest of reeds. The six Krittikas beheld that child of theirs looking like the morning sun in splendour. Filled with affection for him,--indeed, loving him very much,--they began to rear him with the sustenance of their breasts. In consequence of his having been born of the Krittikas and reared by them, he came to be known throughout the three worlds as Kartikeya. Having sprung from the seed which had fallen off from Rudra he was named Skanda, and because of his birth in the solitude of a forest of reeds he came to be called by the name of Guha (the secret-born).