From Sahih Bukhari (Hadith 1875):
Narrated Sufyan b. Abu Zuhair:I heard Allah's Messenger (ﷺ) saying, "Yemen will be conquered and some people will migrate (from Medina) and will urge their families, and those who will obey them to migrate (to Yemen) although Medina will be better for them; if they but knew. Sham will also be conquered and some people will migrate (from Medina) and will urge their families and those who will obey them, to migrate (to Sham) although Medina will be better for them; if they but knew. 'Iraq will be conquered and some people will migrate (from Medina) and will urge their families and those who will obey them to migrate (to 'Iraq) although Medina will be better for them; if they but knew
Reference: Bukhari 1875