Lady Umm Hani (may Allah be pleased with her) narrates: The Noble Prophet (peace and blessings be upon him) came to her, and a vessel was brought to him, so he drank from it. Then he passed the vessel to me. I said: I am fasting. The Noble Prophet (peace and blessings be upon him) said: "A person observing a voluntary fast is the master of his own decision (the narrator is in doubt, perhaps the words are: the trustee of his own self). If you wish, keep the fast, and if you wish, then eat and drink."
Hadith Referenceسنن الدارقطني / كتاب الصيام / 2222
Hadith Takhrij«أخرجه البيهقي فى((سننه الكبير)) برقم: 8084، 8085، والدارقطني فى ((سننه)) برقم: 2220، وابن أبى شيبة فى ((مصنفه)) برقم: 9543»