Sayyiduna Shuraid (may Allah be pleased with him) said: I presented myself before the Prophet (peace and blessings be upon him) and said that my mother (lady) has to offer expiation for freeing a slave, and I have a black Abyssinian slave-girl; will she suffice? The Prophet (peace and blessings be upon him) said: "Bring her to me." When she came, the Prophet (peace and blessings be upon him) said: "Do you testify to «لا إله إلا اللّٰھ»?" She said: Yes. He said: "Go, set her free, for she is a believer."
Hadith Referenceسنن دارمي / من النذور و الايمان / 2385
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده حسن من أجل محمد بن عمرو، [مكتبه الشامله نمبر: 2393]
Hadith Takhrijاس حدیث کی سند حسن ہے۔ دیکھئے: [ابن حبان 189] ، [موارد الظمآن 1207]
Brief Explanation
(Commentary on Hadith 2384) In the expiation (kaffarah) of an oath, the command is to free a neck (i.e., a slave), whether male or female. Similarly, in unintentional killing (qatl-i-khata), along with the blood money (diyah), the command is also to free a neck, and there the condition of the slave being a believer (mu’minah) is stipulated (Surah al-Nisa 92). Here, in this hadith as well, the command is to free a believing slave (raqabah mu’minah). Furthermore, it is understood from the hadith that a man can be freed in exchange for a woman, or a woman in exchange for a man, if they are Muslims.