Ja’far As-Saa-igh (rahimahullah) narrates the following:
Among the neighbours of Imaam Ahmad bin Hambal (rahimahullah) was a man who was involved in many sins, evils and shameless deeds. One day, this man came to the gathering of Imaam Ahmad bin Hambal (rahimahullah) and greeted him with salaam. Although Imaam Ahmad (rahimahullah) replied to his salaam, he did not show him attention and receive him with warmth. Rather, he seemed uncomfortable in the presence of this man (as this man was well known to have evil ways and sinful habits).
The man immediately perceived the discomfort of Imaam Ahmad (rahimahullah) and thus said, “O Abu ‘Abdillah (rahimahullah)! Why are you uncomfortable in my presence? On account of a dream that I saw, I have completely changed and I am no longer the person that you knew me to be.” Imaam Ahmad (rahimahullah) asked, “What dream did you see?”
The man replied, “I saw Rasulullah (sallallahu ‘alaihi wasallam) in my dream. It seemed as though he was on an elevated area while many people were seated below him. One by one, the people stood and asked Rasulullah (sallallahu ‘alaihi wasallam) to make du‘aa for them. As they stood and made their request, Rasulullah (sallallahu ‘alaihi wasallam) made du‘aa for them, until only I remained.
“I also wanted to stand and ask Rasulullah (sallallahu ‘alaihi wasallam) to make du‘aa for me, but I felt embarrassed and ashamed to do so on account of my evil actions and ways. Rasulullah (sallallahu ‘alaihi wasallam) then addressed me and asked, “O so-and-so! Why do you not stand and ask me to make du‘aa for you?” I replied, “O Rasul of Allah (sallallahu ‘alaihi wasallam)! It is my shame and embarrassment of my evil deeds that prevents me from doing so.”
“Rasulullah (sallallahu ‘alaihi wasallam) responded, “If it is shame and embarrassment that prevents you, then stand and ask me for du‘aa. I will still make du‘aa for you, as you love my Sahaabah (radhiyallahu ‘anhum) and do not speak ill of them.” I thus stood and Rasulullah (sallallahu ‘alaihi wasallam) made du‘aa for me.
“When I thereafter awoke, I found that Allah Ta‘ala had instilled within me complete hatred and disgust for all the sins that I was involved in.”
When Imaam Ahmad (rahimahullah) heard this incident, he addressed us saying, “O Ja’far! O so-and-so! Tell people of this incident and do not forget it, as it is beneficial and inspiring.” (Kitaabut Tawwaabeen – Ibnu Qudaamah pg. 157-158)