Sahih Bukhari Volume 8, Book 78, Hadith 6029

وَكَانَ النَّبِيُّ صلى الله عليه وسلم جَالِسًا إِذْ جَاءَ رَجُلٌ يَسْأَلُ أَوْ طَالِبُ حَاجَةٍ أَقْبَلَ عَلَيْنَا بِوَجْهِهِ فَقَالَ ‏"‏ اشْفَعُوا فَلْتُؤْجَرُوا، وَلْيَقْضِ اللَّهُ عَلَى لِسَانِ نَبِيِّهِ مَا شَاءَ ‏"‏‏.‏

The Prophet then clasped his hands with the fingers interlaced. (At that time) the Prophet was sitting and a man came and begged or asked for something. The Prophet faced us and said, "Help and recommend him and you will receive the reward for it, and Allah will bring about what He will through His Prophet's tongue."