سورة Al-Baqarah ( The Cow ) - الآية 229

Divorce may be pronounced twice; then either retaining in all kindness, or separating in the best way. It is not lawful for you to take back anything that you have given them [of dowry], except when they both fear that they would not be able to maintain the limits ordained by Allah. So if you fear that they would not be able to maintain the limits set by Allah, then there is no sin upon either of them if she opts to give something for her release[121]. These are the limits ordained by Allah, so do not exceed them; whosoever exceeds the limits ordained by Allah, it is they who are the wrongdoers.