الكافي 2/1/83/5

5. A number of our people have narrated from Ahmad ibn Muhammad ibn Khalid from his father from Harun ibn al-Jahm from Isma’il ibn ‘Ammar al-Sayrafi who has said the following: “Once I asked Abu ‘Abdillah عليه السلام ‘May Allah keep my soul in service for your cause, is a believer a blessing for believers?’ The Imam said, ‘Yes, he is.’ I then asked, ‘How is he as such?’ The Imam said, ‘A believer who may come to his brother (in belief) for help, in fact, is a blessing from Allah whom He has lead to him and has made him a means of blessings for him. If he makes his wish come true he accepts the blessing through his help and if he refuses to help while capable to help he, in fact, has repulsed from himself blessings that Allah, the Most Majestic, the Most Holy, had lead to him and had made him (believer) a means for his receiving rewards. Allah, the Most Majestic, the Most Holy, preserves that blessing to the Day of Judgment so that the needy believer who had faced refusal may decide about it. He may avail it for himself or someone else. O Isma’il, on the Day of Judgment when he will be the judge for the blessing from Allah that is appropriated to him to who do you think he will make it available?’ I said, ‘I do not think he will turn it away from himself.’ The Imam said, ‘Do you not think? Be certain that he will not turn it away from himself. O ’Isma’il, if a believer comes to his brother (in belief) for help and he refuses to help, despite being able to help, in his grave Allah will raise a snake to keep biting his thumb to the Day of Judgment wherein he may be forgiven or made to suffer torments.’”