Mishkat al-Masabih 5907 — Excellent Qualities and Description of the Prophet

He told that Umm Malik used to present clarified butter to the Prophet in a skin of hers. Her sons would come to her and ask for seasoning when they had nothing, and she would go to the skin from which she made presents to the Prophet and find clarified butter in it. It kept providing her with seasoning for her household till she squeezed it, so she went to the Prophet who asked whether she had squeezed it, and when she replied that she had, he said, "If you had left it alone it would have kept on as it was." Muslim transmitted it.