Abbad bin Abdullah al-Asadi (may Allah have mercy on him) said that Sayyiduna Ali (may Allah be pleased with him) said: When a free woman is married while there is a slave woman (as wife), two days are to be assigned to her, whereas the slave woman will be given one day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14750