Hadith 1170B5

قَالَ مَالِكٌ : وَالْعَبْدُ بِمَنْزِلَةِ الْحُرِّ فِي قَذْفِهِ وَلِعَانِهِ، يَجْرِي مَجْرَى الْحُرِّ فِي مُلَاعَنَتِهِ، غَيْرَ أَنَّهُ لَيْسَ عَلَى مَنْ قَذَفَ مَمْلُوكَةً حَدٌّ .
Imam Malik, may Allah have mercy on him, said: If a man gives his wife three divorces and she admits to being pregnant, and after that he accuses her of adultery, then the punishment of false accusation (hadd al-qadhf) will be imposed on the husband and li'an will not be obligatory for him. However, if after the divorce he denies her pregnancy, then li'an is obligatory. This is what I have heard.
Hadith Reference موطا امام مالك رواية يحييٰ / كتاب الطلاق / 1170B5
Hadith Takhrij «فواد عبدالباقي نمبر: 29 - كِتَابُ الطَّلَاقِ-ح: 35»