The Prophet ﷺ said, "When one of you marries his slave to his slave-girl, he should not look at her private parts."
حدثنا محمد بن عبد الله بن الميمون حدثنا الوليد عن الأوزاعي
عن النبي ﷺ قال إذا زوج أحدكم عبده أمته فلا ينظر إلى عورتها
[Hasan] See the following hadith. Bayhaqi 2/226 also narrated it from the hadith of Abu Dawud, with the same wording.