Allah's statement,

﴿وَيُرْبِى الصَّدَقَـتِ﴾

(And will give increase for Sadaqat) means, Allah makes charity grow, or He increases it. Al-Bukhari recorded that Abu Hurayrah said that the Messenger of Allah said,

«مَنْ تَصَدَّقَ بِعَدْلِ تَمْرَةٍ مِنْ كَسْبٍ طَيِّبٍ، وَلَا يَقْبَلُ اللهُ إِلَّا الطَّيِّبَ، فَإِنَّ اللهَ يَتَقَبَّلُهَا بِيَمِينِهِ، ثُمَّ يُرَبِّيهَا لِصَاحِبِهِ، كَمَا يُرَبِّي أَحَدُكُمْ فَلُوَّهُ حَتَّى تَكُونَ مِثْلَ الْجَبَل»

(Whoever gives in charity what equals a date from honest resources, and Allah only accepts that which is good and pure, then Allah accepts it with His right (Hand) and raises it for its giver, just as one of you raises his animal, until it becomes as big as a mountain.)

This was recorded in the book of Zakah.