Drawing evidence from what we have narrated in the established hadith from Sayyidah Aishah and Sayyiduna Abu Hurayrah (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "The child belongs to the (owner of the) bed, and for the fornicator is the stone (deprivation)."
So he (peace and blessings be upon him) did not give the fornicator's fluid (semen) any sanctity.
Sa'id bin al-Musayyib (may Allah have mercy on him) narrates from an Ansari Companion named Basrah (may Allah be pleased with him), who says: I married a virgin woman who was in her seclusion. When I went in to her, she was pregnant. The Prophet (peace and blessings be upon him) said to me: "She is owed the dower for what you made lawful of her private part, and the child will be your slave; and when she gives birth, flog her."
The Shaykh (may Allah have mercy on him) says: Ibn Jurayj took this hadith only from Ibrahim bin Abi Yahya, from Safwan bin Sulaym, and there is disagreement about Ibrahim's integrity.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13889