Mishkat al-Masabih 2957
Rafi' b. 'Amr al-Ghifari said:
When I was a boy I used to throw stones at the palm-trees belonging to the Ansar and was brought to the Prophet. He asked, “Why do you throw stones at the palm-trees, boy?” and when I replied that it was to get something to eat he said, “Do not' throw stones, but you may eat anything that falls below them.” Then passing his hand over my head he said, “O God, fill his belly.” 

Tirmidhi, Abu Dawud and Ibn Majah transmitted it.
وَعَن رَافع بن عَمْرو الْغِفَارِيّ قَالَ: كُنْتُ غُلَامًا أَرْمِي نَخْلَ الْأَنْصَارِ فَأُتِيَ بِيَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ: «يَا غُلَامُ لِمَ تَرْمِي النَّخْلَ؟» قُلْتُ: آكُلُ قَالَ: «فَلَا تَرْمِ وَكُلْ مِمَّا سَقَطَ فِي أَسْفَلِهَا» ثُمَّ مَسَحَ رَأْسَهُ فَقَالَ: «اللَّهُمَّ أَشْبِعْ بَطْنَهُ» . رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَابْنُ مَاجَهْ