الكافي 2/1/83/13

13. Al-Husayn ibn Muhammad has narrated from Mu’alla ibn Muhammad from Ahmad ibn Muhammad ibn ‘Abd Allah from Ali ibn Ja’far who has said the following: “I heard abu al-Hassan عليه السلام saying, ‘To whomever his believing brother (in belief) comes for help, in fact, it is a blessing from Allah, the Most Blessed, the Most High, that He has lead to him. If he accepts that blessing he has connected his guardianship with our guardianship ( al - Walayah ) that is connected to the guardianship of Allah. If he refuses to help when he is able to help, Allah assigns a snake from fire to keep biting him in his grave until the Day of Judgment wherein he will be forgiven or made to suffer torment. If in such case (in need of help) the needy accepts his excuse it will be much worse for him.’”