It is narrated from Imam Ali (AS) who narrated from the Prophet of Islam (PBUH) who said:

(The reward) for Sadaqah is calculated as ten times, and lending as 18 times, and helping friends and brothers 20 times and keeping ties with family and relatives 24 times [1]. When someone pays Sadaqah, he/she is rewarded ten times (by Allah (SWT); but when you lend money to someone, God will reward you 18 times, because receiver of Sadaqah does not need to do anything else, but the one who borrows money needs to work and find money to pay for the debt; this is encouragement to do work and also keep good ties and social relations with family and friends

[1] Navader-e-Ravandi, Page 95.

Source: en.shafaqna.com