Ibrahim and al-Sha'bi (may Allah have mercy on them both) said: When non-Muslims bring their case to the Muslim rulers, then if they wish they may judge, and if they do not wish they may not; and if they judge, they judge according to the ruling Allah has revealed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 17114