An-Nisa 4:3

Wa-in khiftum alla tuqsitoo feealyatama fankihoo ma tabalakum mina annisa-i mathna wathulathawarubaAAa fa-in khiftum alla taAAdiloo fawahidatanaw ma malakat aymanukum thalika adnaalla taAAooloo

And if you fear that you will not deal justly with the orphan girls, then marry those that please you of [other] women, two or three or four. But if you fear that you will not be just, then [marry only] one or those your right hands possess [i.e., slaves]. That is more suitable that you may not incline [to injustice].

If you fear that you will not do justice to the orphans, then, marry the women you like, in twos, in threes and in fours. But, if you fear that you will not maintain equity, then (keep to) one woman, or bondwomen you own. It will be closer to abstaining from injustice.