Muhammad Bin Saaib Al Kalbi narrates in his book (Al Salabah Fe Ma'rifat Al Sahabah) (3/212)
... Nufayl was working for Kalb Bin Luayy Bin Ghalib AlQarshy and he (Kalb) died. His new master was Abdul Muttalib, Sahak was also working for Abdul Mutalib she was shepherd taking care of his sheep. He separated between them in the pasture and they agreed one day to meet in a rest home. Nufayl desired and loved her. Abdul Muttalib had made her put on pants of leather with a lock on and he kept its key with him to her status of him. When he (Nufayl) chased her she said: nothing from what you are saying is for me and he has made me put this leather and put a lock on it. He said: I can trick him, he took some butter from the sheep's buttermilk and smeared the leather and what is around it of her body with the butter till slipped down to her thighs. He did effect her and she got pregnant by him with Al Khattab. When she had given birth to him she threw him on some garbage during the night with fear of Abdul Muttalib. A Jewish woman named Jenazah picked up Al Khattab and raised him. When he grew up he used to cut wood and was named 'Al Hattab' the wood cutter. So with the letter 'Ha' but was distorted in the vocabulary. Sahak was faring him in secrecy, one day he saw her and her bottom was lowered. He didn't know who she was, he fell on her and she got pregnant by him with Hantamah. When she had given birth to her she threw her in the dumps outside of Makkah. Hisham Bin Magheer Bin Walid picked her up and raised her and she was attributed to him. When she grew up and Al Khattab frequently visited Hisham and he saw Hantamah and liked her. He asked Hisham if he could marry her and Hisham allowed her to marry him. She gave birth to Omar. Al Khattab was Omar's father because he and Hantamah got married and she gave birth to him. And at the same time his grandfather because he and Sahak got Hantamah. Al khattab and Hantamah are from the same mother Sahak.
And we summarize the lineage of Omar Bin Al Khattab as follows:
Nufayl + Sahak = Al Khattab
Al Khattab + Sahak = Hantamah
Al Khattab + Hantamah = Omar
We see that Hantamah is the mother and sister of Omar Bin Al Khattab i.e. she is the wife and the daughter of Al Khattab.
And Al Khattab is his father because he is Sahak's lover (i.e. who committed fornication with her) and her son at the same time. I.e. he is Omar's father and grandfather at the same time.
Sahak is his grandmother, mother of his father and the mistress of his father at the same time.
Al Salabah Fe Ma'rifat Al Sahabah (3/212)
Ilzam Al Nawasib. By : Nurullah Zarihi.
Volume 1, Book 3, Number 92 :
Narrated by Abu Musa
The Prophet was asked about things which he did not like, but when the questioners insisted, the Prophet got angry. He then said to the people, "Ask me anything you like." A man asked, "Who is my father?" The Prophet replied, "Your father is Hudhafa." Then another man got up and said, "Who is my father, O Allah's Apostle ?" He replied, "Your father is Salim, Maula (the freed slave) of Shaiba." So when 'Umar saw that (the anger) on the face of the Prophet he said, "O Allah's Apostle! We repent to Allah (Our offending you)."
Volume 1, Book 3, Number 93 :
Narrated by Anas bin Malik
One day Allah's Apostle came out (before the people) and 'Abdullah bin Hudhafa stood up and asked (him) "Who is my father?" The Prophet replied, "Your father is Hudhafa." The Prophet told them repeatedly (in anger) to ask him anything they liked. 'Umar knelt down before the Prophet and said thrice, "We accept Allah as (our) Lord and Islam as (our) religion and Muhammad as (our) Prophet." After that the Prophet became silent.