Sahih Muslim Book 6, Hadith Number 2478.
Chapter : Permissibility of observing the fast or not observing it in the month of Ramadan for a traveller.
A Hadith like this has been narrated on the authority of Qatada with the same chain of transmitters by different narrators (except this difference) that in the Hadith transmitted by Taimi and Umar b. Amir and Hisham (the date of setting out is) 18th, and in the Hadith transmitted by Sa’id it is the 12th, and in the one transmitted by Shu’ba it is the 17th or 19th.