Ibn 'Abbas (RAA) narrated that Allah's Messenger (ﷺ) said:
"When a man's slave-woman bears him a child she becomes free at his death." Related by Ibn Majah and Al-Hakim with a weak chain of narrators. (FR)
English reference (FR): Book 15, Hadith 1479 (FR)
Arabic reference (FR): Book 15, Hadith 1435 (FR)