It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) prayed the Fajr prayer on a journey, he would walk a little away from his mount."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4748
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حل هق] عن أنس. الصحيحة ٢٠٧٧: طس، الضياء.