I read in a letter of Abdallah b. Muhammad to Abi al-Hasan عليه السلام [the following]: our fellows have differed in their narration from Abi Abdillah عليه السلام in regards the two units of Fajr whilst travelling, some of them narrated ‘pray them in your litter’ while others narrated ‘do not pray them except stationary on the ground’ so inform me what you personally do so that I can follow you in it? he wrote: it is accommodating for you whichever of them you act by.