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 ‏"‏ ‏.‏

It was narrated from Umm Salamah that the Prophet (PBUH) 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.” Translation Not Available

Book reference: Sunan Ibn Majah Book 19 Hadith 2520
Web reference: Sunan Ibn Majah Volume 3 Book 19 Hadith 2520