Comprehension, language, and application

What kind of expression is «كَيَوْمِ وَلَدَتْهُ أُمُّهُ»?

Rights of Guests and Neighbors, Worship, Sincerity, and Responsible Care (Hadith 246–252)

• A list of property
• A comparison with the day of birth
• An interrogative sentence
• Negation of a past verb