Abu Dawud Book 2, Hadith Number 1200.

Chapter : On offering prayer by a traveller during journey while has doubt about its correct timing.

Narated By Mishaj b. Musa : I asked Anas b. Malik: Narrate to us what you heard the Apostle of Allah (PBUH) say. He said: When you travelled along with the Apostle of Allah (PBUH), we would say: Did the sun pass the meridian or not? But he (the Prophet) would offer the noon prayer and then proceed.