Hadithcore
Mishkat al-Masabih, 3289

‘A’isha reported God’s Messenger as saying, “The divorce of a slave-woman consists in saying it twice, and her <i>'idda</i> period is two courses.” Tirmidhi, Abu Dawud, Ibn Majah and Darimi transmitted it.

وَعَنْ عَائِشَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «طَلَاقُ الْأَمَةِ تَطْلِيقَتَانِ وَعِدَّتُهَا حَيْضَتَانِ» . رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَابْنُ مَاجَهْ وَالدَّارِمِيُّ

References1 variant
In-Book Reference
Book 13, Hadith 204