Al-Muwatta de Malik, 350

Nafé a rapporté que Abdallah Ibn Omar, ne faisait, en voyageant, avec la prière prescrite, aucune autre prière, ni même avant elle, ni après, sauf au milieu de la nuit; car il faisait la prière sur la terre ou sur la monture quelque soit sa direction»

Yahya related to me from Malik from Nafi that Abdullah ibn Umar never used to pray anything with the fard prayer, either before it or after it, while travelling, except in the depths of the night. He would pray on the ground or on his mount, whichever way it was facing