Sahih Al Bukhari Hadith Number 1913

Narrated Ibn `Umar: The Prophet (peace be upon him) said, “We are an illiterate nation; we neither write, nor know accounts. The month is like this and this, i.e. sometimes of 29 days and sometimes of thirty days.”

30  Fasting
Hadith number 1913
Volume no 3
Chapter: 13 (“We neither write nor know accounts.”)