Umar bin Abd al-Rahman al-Qurashi narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that he was asked about (freeing) a child born of fornication, and also about freeing a child of legitimate birth. He said: Look! Which of the two has the higher price? So they looked, and the price of the child born of fornication was higher by one dinar, so he ordered them (to free) him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20001