It is narrated from Hazrat Sha'bi (may Allah have mercy on him) that a man contracted marriage on the condition that if he had a wife, the dowry would be two thousand; if not, then one thousand. Later it was found out that he had a wife. Hazrat Sha'bi (may Allah have mercy on him) said: "The woman will receive the lesser dowry."
Hadith Referenceسنن سعید بن منصور / كتاب النكاح / 2195