There are a couple of references that I am aware of that I can share with you, however, the fight probably wasn't before the creation of the earth, because on the sixth day of creation, God said that Everything was Very Good. How could everything be good if there was sin through Satan?
Isaiah 14: 12-15
12 How you have fallen from heaven, O morning star, son of the dawn! You have been cast down to the earth, you who once laid low the nations!
13 You said in your heart, "I will ascend to heaven; I will raise my throne above the stars of God; I will sit enthroned on the mount of assembly, on the utmost heights of the sacred mountain.
14 I will ascend above the tops of the clouds; I will make myself like the Most High."
15 But you are brought down to the grave, to the depths of the pit.
(Many people think that this is what was said, the "I will's" that spoke rebellion and sin into existence. His statements of pride led to his fall.)
Ezekiel 28: 12-19
12 "Son of man, take up a lament concerning the king of Tyre and say to him: 'This is what the Sovereign LORD says: "'You were the model of perfection, full of wisdom and perfect in beauty.
13 You were in Eden, the garden of God; every precious stone adorned you: ruby, topaz and emerald, chrysolite, onyx and jasper, sapphire, turquoise and beryl. Your settings and mountings were made of gold; on the day you were created they were prepared.
14 You were anointed as a guardian cherub, for so I ordained you. You were on the holy mount of God; you walked among the fiery stones.
15 You were blameless in your ways from the day you were created till wickedness was found in you.
16 Through your widespread trade you were filled with violence, and you sinned. So I drove you in disgrace from the mount of God, and I expelled you, O guardian cherub, from among the fiery stones.
17 Your heart became proud on account of your beauty, and you corrupted your wisdom because of your splendor. So I threw you to the earth; I made a spectacle of you before kings.
18 By your many sins and dishonest trade you have desecrated your sanctuaries. So I made a fire come out from you, and it consumed you, and I reduced you to ashes on the ground in the sight of all who were watching.
19 All the nations who knew you are appalled at you; you have come to a horrible end and will be no more.'"
(This is God speaking through Ezekiel vs. 11. Most scholars think that the king of Tyre is symbolism for Satan because the king obviously was not in the garden of Eden. Because Satan is the ruler of this world, he wants to be where the power is, and at that time in history, Tyre was powerful. Of course, later in Ezekiel, God judged the city and said it would be no more, and now it does not exist. So in order for Satan to be a 'cherub in Eden', it is my opinion that the fall happened after Creation.)
I hope these help. I also like to know the answer to questions like these. I love to research. I don't think that it takes the focus off of Jesus. He knows our curiousness, our doubts, and thankfully He doesn't leave us in the dark about everything.
1 Peter 3: 15 But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect,
I think we must be prepared, must be 'up to date' with our Bible reading and understanding in order to answer questions. I work at a church, and I love it when people call me, saying that someone asked them a question that they didn't have an answer for but hoped that someone could help. These are valid issues. Don't be afraid to search for answers because your searching for answers led you to Jesus and it could do the same for your friend. Jesus and our faith holds up under scrutiny.
