ENOfficial
Bahz bin Hakim narrated from his father that his grandfather said: "If something was brought to him, the prophet would ask whether it was a gift or charity. If it was said that if was charity, he would not eat, and if it was said that it was a gift, he would stretch forth his hand."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا زِيَادُ بْنُ أَيُّوبَ، قَالَ حَدَّثَنَا عَبْدُ الْوَاحِدِ بْنُ وَاصِلٍ، قَالَ حَدَّثَنَا بَهْزُ بْنُ حَكِيمٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا أُتِيَ بِشَىْءٍ سَأَلَ عَنْهُ " أَهَدِيَّةٌ أَمْ صَدَقَةٌ " . فَإِنْ قِيلَ صَدَقَةٌ لَمْ يَأْكُلْ وَإِنْ قِيلَ هَدِيَّةٌ بَسَطَ يَدَهُ .
sunnah.com