An-Nisa · 4:3

3. If you fear that you will not be just in marrying the female orphans under your guardianship – fearing that you will not give them an appropriate dowry or will not treat them well – then do not marry them, and marry other women you choose. You may marry two, three or four; but if you fear that you will be unjust between them, then marry just one, or suffice with what you possess of slave women, for their rights are not the same as the rights of wives. This is the best way to avoid being unjust or biased.