Yahya related to me from Malik that he had heard that Said ibnal-Musayyab was asked whether a man who had vowed to fast a monthcould fast voluntarily, and Said said, "He should fulfil his vowbefore he does any voluntary fasting."Malik said, "I haveheard the same thing from Sulayman ibn Yasar."Malik said,"If someone dies with an unfulfilled vow to free a slave or to fast orto give sadaqa or to give away a camel, and makes a bequest that hisvow should be fulfilled from his estate, then the sadaqa or the giftof the camel are taken from one third of his estate. Preference isgiven to it over other bequests, except things of a similar nature,because by his vow it has become incumbent on him, and this is not thecase with something he donates voluntarily. They (vows and voluntarydonations) are settled from a limited one-third of his estate, and notfrom the whole of it, since if the dying man were free to dispose ofall of his estate, he might delay settling what had become incumbenton him (i.e. his vows), so that when death came and the estate passedinto the hands of his heirs, he would have bequeathed such things(i.e. his vows) that were not claimed by anyone (like debts). If that(i.e. to dispose freely of his property) were allowed him, he woulddelay these things (i.e. his vows) until when he was near death, hewould designate them and they might take up all of his estate. He mustnot do that."
USC-MSA web (English) reference: Book 18, Hadith 42
Arabic reference: Book 18, Hadith 674