During the life of the Prophet there was no pressing need to write down all of
his various statements or record his actions because he was present and could be
consulted at any time. As a matter of fact, the Prophet himself made a general
prohibition against writing down his statements which were other than the
Qur’aan itself. This was to prevent the possibility of mixing up the Qur’aan with
his own words during the era of revelation. Consequently, the greatest stress
regarding writing was placed on recording the Qur’aanic verses. However, there
are many authentic narrations collected by the Scholars of Hadeeth that prove that Hadeeth were recorded in writing even during the lifetime of the Prophet. For
example, ‘Abdullaah ibn ‘Amr said: “I used to write everything which I heard
from the Messenger of Allaah with the intention of memorizing it. However,
some Qurayshites forbade me from doing so saying, ‘Do you write everything
that you hear from him, while the Messenger of Allaah is a human being who
speaks in anger and pleasure?’ So I stopped writing, and mentioned it to the
Messenger of Allah. He pointed with his finger to his mouth and said: ‘Write!
By Him in whose hand is my soul, only truth comes out from it.’Aboo Hurayrah said: When Makkah was conquered, the Prophet stood up and gave a sermon [Aboo Hurayrah then mentioned the sermon]. A man from
Yemen, called Aboo Shaah got up and said, “O Messenger of Allaah! Write it
down for me.” The Messenger of Allaah replied, “Write it for Aboo Shaah.” Al-Waleed asked Aboo ‘Amr, “What are they writing?” He replied, “The sermon
which he heard that day.” Aboo Qaabeel said: We were with ‘Abdullaah ibn ‘Amr ibn al-‘Aas and he was asked which city will be conquered first Constantinople or Rome? So ‘Abdullaah called for a sealed trunk and he said, “Take out the book from it.” Then ‘Abdullaah said, “While we were with the Messenger of Allaah writing,
The Messenger of Allaah was asked, “Which city will be conquered first,
Constantinople or Rome?” So Allaah’s Messenger said: “The city of Heracilius will be conquered first,” meaning Constantinople.”
[Taken from Dr. Abu Ameenah Bilal Philips' book Usool al-Hadeeth]