Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "O Mu'adh bin Jabal! When a man says to his wife: 'You are divorced, if Allah wills', she is not divorced; but when he says to his slave: 'You are free, if Allah wills', then he is free."
Only Humayd bin Malik narrated it, and he is majhul (unknown). There is disagreement over its chain from him: it is said as above; it is said: from him, from Makhul, from Malik bin Yukhamir, from Mu'adh; and it is said: from him, from Makhul, from Mu'adh, which is munqati' (broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19923