Prayer (Kitab Al-Salat): Detailed Rules of Law about the Prayer during Journey
Dawud :: Book 4 : Hadith 1273
Narrated Abdullah ibn Umar:
Yasar, the client of Ibn Umar, said: Ibn Umar saw me praying after the break of dawn. He said: O Yasar, the Apostle of Allah (peace_be_upon_him) came to us while we were offering this prayer. He (the Prophet) said: Those who are present should inform those who are absent: Do not offer any prayer after (the break of) dawn except two rak'ahs.