ENOfficial
It was narrated from Umm Salamah that the Prophet (ﷺ) said: “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.”
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنِ الزُّهْرِيِّ، عَنْ نَبْهَانَ، - مَوْلَى أُمِّ سَلَمَةَ - عَنْ أُمِّ سَلَمَةَ، أَنَّهَا أَخْبَرَتْ عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ " إِذَا كَانَ لإِحْدَاكُنَّ مُكَاتَبٌ وَكَانَ عِنْدَهُ مَا يُؤَدِّي فَلْتَحْتَجِبْ مِنْهُ " .
sunnah.com