Sahih Muslim
The Book Pertaining to the Excellent Qualities of the Holy Prophet (may Peace be upon them) and His Companions (Kitab Al-Fadail)
Book Number: 030 / Hadith Number: 5698
A hadith like this has been transmitted on the authority, of 'Ubaidullah with this addition: Ubaidullah was asked (about these two names, i. e. Jarba' and Adhruh). He said: These are the two towns of Syria and there is between them the distance which can be covered in three nights, and the hadith transmitted on the authority of Ibn Bishr (the words are)." Three days."