Ibn Jurayj (may Allah have mercy on him) narrates from Ata (may Allah have mercy on him) that it reached him from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "No more than what was given should be taken from a woman who seeks khul'."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14846