And the Prophet Muhammad (peace be upon him) said: Allah the Exalted has stated, "Whatever I have not decreed, the vow of the son of Adam cannot bring it to him. However, through a vow, I extract wealth from a miser; he gives Me what he would never give in his state of miserliness." And the Prophet Muhammad (peace be upon him) said: Allah the Exalted says, "(O son of Adam) spend, I will spend on you."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 8152