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Buhaisa quoted her father as saying that he asked God’s messenger what was the thing which it is unlawful to refuse and was told that it was water. He repeated the question to God’s Prophet and was told that it was salt. When he asked God’s Prophet a third time he received the reply, “To do good is better for you.” Abu Dawud transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ بُهَيْسَةَ عَنْ أَبِيهَا قَالَتْ: قَالَ: يَا رَسُول الله مَا لشَيْء الَّذِي لَا يَحِلُّ مَنْعُهُ؟ قَالَ: «الْمَاءُ» . قَالَ: يَا نَبِيَّ اللَّهِ مَا الشَّيْءُ الَّذِي لَا يَحِلُّ مَنْعُهُ؟ قَالَ: «الْمِلْحُ» . قَالَ: يَا نَبِيَّ الله مَا لاشيء الَّذِي لَا يَحِلُّ مَنْعُهُ؟ قَالَ: «أَنْ تَفْعَلَ الْخَيْر خير لَك» . رَوَاهُ أَبُو دَاوُد
sunnah.com