It is narrated from Imam Ali (AS) who said:

When the Prophet of Islam (PBUH) sent me to Yemen, told me: O’ Ali, do not fight any one unless you invite that person to Islam first. Swear to Allah (SWT), if God guides one person through you, it is worth more than all the wealth on the earth, and you will have Welayah on that person [1]. The importance of guiding a person to the path of Allah (SWT) is worth more than all the wealth on the earth; this can be understood from the spiritual point that Divine Guidance is so important for any human being that if another person can facilitate this process, no other material case can be compared with it.

[1] Navader Ravandi, Page 139.

Source:en.shafaqna.com