Narrated Amr bin Suhaib: On his father's authority, said that his grandfather reported the Prophet ﷺ said: When one of you marries his male-slave to his slave-woman, he should not look at her private parts.
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues:
The owner has the right to derive sexual benefit from his slave woman, but when he relinquishes his right and marries her off, then it becomes forbidden for him even to look at the private parts specific to her.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 4114