How sound are the narrations mentioned about Uthman (may Allah be pleased with him), and is the author of the booklet correct in his ruling allowing Murabaha sales with a percentage?

Murabaha sale is the sale of a commodity for its cost price plus a known profit. If the profit is a fixed amount (e.g., "I sell it to you for my cost price, which is one hundred, and my profit is ten"), it is permissible by consensus, without any disfavor. However, if the profit is a percentage (e.g., "I sell it to you for my cost price, which is one hundred, and I profit one dirham for every ten," or "My profit is 10% of the price"), some early scholars disliked it, and Ishaq did not permit it. Nevertheless, the majority of scholars, such as Al-Shafi'i, the jurists of opinion (Ahl al-Ra'y), and Ibn al-Mundhir, permitted it because both the cost price and the profit are known, and the ambiguity can be removed through calculation.