In the beginning of the world there were Manu and Shatroopaa who had two sons - Uttaanpaad and Priyavrat. Uttaanpaad had a son named Dhruv. Manu had three daughters also: Aakooti, Devhooti and Prasooti. The same Manu and Shatroopaa did a very hard Tap on the banks of Dhenumatee River for several thousand years. Seeing this all three - Brahmaa, Vishnu and Mahesh, came to give them Var but they did not move from their intentions. Then there was Aakaashvaanee (celestial voice) - "Hey Raajan, ask for any Var".

Manu got very happy to hear this voice, he said - "If you are indeed pleased with us then show us the same Roop (form) which Shiv Jee meditate up on. Muni have to do a lot of Tapasyaa to see that Roop; which is in the heart of Kaagbhushundi Jee and Ved admire it describing as Sa-Gun and Nir-Gun. We want to see your same Roop."

Bhagvaan appeared before them along with His Aadi Shakti (initial power) from whom many Umaa, Lakshmee Jee and Brahmaanee have appeared. He said - "I am very pleased with you ask for any Var. There is nothing I cannot give you." Manu said - "I wish for a son like you." Bhagvaan said - "Now where will I go to look for a son like me? So I myself will appear as your son."

Then Bhagvaan glanced at Shatroopaa who was standing folding her hands. Bhagvaan asked her also to ask for a Var. She said - "Whatever my husband has asked for I liked that Var, but give me same Bhakti, same Gati, same knowledge, same love towards your feet which you give to your own Bhakt." Bhagvaan said - "Whatever you asked for, I gave it all to you. You will get motherly pleasure and you will have the knowledge too."

Manu said again - "Hey Bhagvan, I have one more wish that I should have the same love towards my son as much I have towards your feet. My life should depend on you as fish depends on water." Bhagvaan said - "So be it. Now you go to Indra Puree and live there for some time. When you will be the king of Ayodhyaa, then I will appear in your house with my Ansh (part) Avataar and Aadi Shakti will also appear with me." After saying this Bhagvaan disappeared and Manu and Shatroopaa went to Amaraavatee.

Thus Manu and Shatroopaa were born as king Dashrath and queen Kaushalyaa, and Raam was Vishnu's Avataar along with His part Avataar - Lakshman, Bharat and Shatrughn appeared in his house.

My Note
I do not understand that whose Avataar were Dashrath and Kaushalyaa? Kashyap and Aditi? or Manu and Shatroopaa? Any help is appreciated.