Surah 4. An-Nisaa', Ayah 89

See surah {2}, note [203], as well as note [124] of this surah.

I.e., any of those who have not "forsaken the domain of evil" and are wavering between belief and disbelief.

 The verse discusses a group of people who nominally became Muslims and secretly supported the enemies of Muslims. For those hypocrites to prove their loyalty, they were commanded to emigrate and join the ranks of the believers, or they would be considered enemies.

Flee: the verbal form which the noun hijrat is derived. Bukhari interprets this rightly as fleeing from all that is forbidden. This would include hijrat in the technical sense of leaving a place in which the practice of religion is not allowed. But it is more general. In time of war, if a man is willing to submit to discipline and refrain from infringing orders issued, he has proved his fidelity and may be treated as a member of the community at war. On the other hand if he by false pretences comes into the inner counsels merely to betray them, he may rightly be treated as a traitor or deserter and be punished for his treason or desertion; or if he escapes, he can be treated as an enemy and is entitied to no mercy. He is worse than an enemy: he has claimed to be of you in order to spy on you, and been all the time helping the enemy.