Musnad Ahmad 28:337

Waki' narrated to us, Mas'udi narrated to us, from 'Amr ibn Murrah, from 'Abdullah ibn al-Harith al-Maktab, from Abu Kathir al-Zubaydi, from 'Abdullah ibn 'Amr, that a man asked the Messenger of Allah, peace and blessings of Allah be upon him: "Which migration is best?" He said: "That you migrate from what your Lord dislikes. And they are two migrations: the migration of the dweller (in the city) and the migration of the bedouin. As for the migration of the bedouin: he obeys when he is commanded, and he answers when he is called. And as for the migration of the dweller: it is the more severe of the two in trial, and the greater of the two in reward."