Sahih BukhariVolume 5, Book 59, Number 602

Narrated 'Ata' bin Abi Rabah:

'Ubaid bin 'Umar and I visited 'Aisha, and he asked her about the migration. She said, "There is no migration today. A believer used to flee with his religion to Allah and His Prophet for fear that he might be put to trial as regards his religion. Today Allah has rendered Islam victorious; therefore a believing one can worship one's Lord wherever one wishes. But there is Jihad (for Allah's Cause) and intentions." (See Hadith 42, in the 4th Vol. for its Explanation)