It is narrated from Imam Baqir (AS) who said: There are three deeds which are considered as the most difficult ones for the servants of God.

1.Fairness/justice of the believer

2.Giving financial help to brethren

3.Remembering God at all the times

In this narration, fairness refers to this point that whatever ways you expect other people to treat you, you treat them the same ways; and whatever you consider appropriate for yourself, consider the same for others and vice-versa. Remembering God at all the times in this narration means, whenever a person is faced with a sin, remembrance of God prevents him/her from committing that sin [1].

[1] Al-Khisal, Sheikh Sadooq (RA), Page 145.

Source: en.shafaqna.com