“If anyone of you (women) has a Mukatab, and he has enough (wealth) to pay off (his contact of manumission), she must veil herself from him.” (Using translation from Ibn Mājah 2520)

أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا كَانَ لِإِحْدَاكُنَّ مُكَاتَبٌ فَكَانَ عِنْدَهُ مَا يُؤَدِّي فَلْتُحْجَبْ مِنْهُ