It is narrated from Malik (may Allah have mercy on him) that it reached him that Sa'id bin al-Musayyib and Sulayman bin Yasar (may Allah have mercy on them both) used to say: The waiting period of a slave woman, when her husband dies, is two months and five nights.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15458