English Translation
Narrated 'Abdullah bin Abbas: The Prophet used to keep his hair falling loose while the pagans used to part their hair, and the People of the Scriptures used to keep their hair falling loose, and the Prophet liked to follow the People of the Scriptures in matters about which he had not been instructed differently, but later on the Prophet started parting his hair.
This hadith is from Sahih al-Bukhari, the most rigorously authenticated collection in Islamic scholarship. No editorial opinion is added.