Central banks unjustly take responsibility for setting the price of money. This usurps one of Allah's roles and giving it to human beings.
The Messenger of Allah (ﷺ) said: Allah is the one Who fixes prices, Who withholds, gives lavishly and provides, and I hope that when I meet Allah, none of you will have any claim on me for an injustice regarding blood or property. 
Sunan Abi Dawud 3451 - Wages (Kitab Al-Ijarah) - كتاب الإجارة - Sunnah.com - Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم)
Hadith of the Prophet Muhammad (saws) in English and Arabic