Musnad Ahmad 33:165

Muhammad ibn Salamah narrated to us, from Hisham, from al-Hasan, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When you travel during a time of plenty, allow the mounts to graze their fill, and do not pass by the stopping places. When you travel during a time of drought, hasten, and you must travel by night, for the earth is folded up by night. When the ghouls (demons) appear to you, hasten to call the Adhan. Beware of praying on the main roads and stopping upon them, for they are the dwelling places of snakes and beasts of prey, and [do not] relieve yourselves upon them, for they are the places of cursing."