What is the basis for saying that Adam was created without sin? I've googled multiple phrases and in different ways, but I haven't yet found any verse that says that Adam an Eve were created without sin. Or that simply says they were without sin before the fall, for that matter.

But I did find multiple scriptures saying Jesus was/is without sin...

It says Adam was made in the image of God...
But so is the rest of humanity.
And we are sinners.

Is it possible that Adam was sinful in nature, but just wasn't held accountable for his sins because he didn't know right from wrong?
Before the fall, when Adam and Eve disobeyed God there was no sin in the world:


  Romans 5:12 through 14 NKJV  Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned— 13  (For until the law sin was in the world, but sin is not imputed when there is no law. 14  Nevertheless death reigned from Adam to Moses, even over those who had not sinned according to the likeness of the transgression of Adam, who is a type of Him who was to come. 


These Scriptures tell us that when Adam and Eve disobeyed God Death came into the world and so did sin, however; sin was not attributed to mankind until God gave Moses the law.

If this sounds confusing try to think of it this way God originally gave Adam instructions not to eat of the tree of the knowledge of good and evil lest they die. Adam by eating from the tree then brought death to mankind. Adam and Eve sinned when they disobeyed God and ate from the tree God told Adam not to eat thereof. However; from the time of their sin until God gave the ten Commandments to Moses no other humans ate from the tree, therefore no others were disobeying God's commandment. Sin is disobeying God. After God punished Adam and Eve, he sort of put man on a trial basis to see if they would use their free will for good or for evil, and that is why God regretted that he had made man and destroyed the World with a flood.

Then after the Flood even though he had chosen righteous Noah to repopulate the World man still gravitated toward evil. 

So the answer to your question must be yes the original man, who we call Adam was created without sin, and did not disobey Cod until they ate from the tree which was the first sin.