"Abdullah bin Mubarak (ra) was an eminent jurist, scholar of Hadith and Sufi of high calibre. He was a contemporary of Imam Abu Hanifah (ra) and his student too. Before he turned to religion he was a very rich and free-thinking man. He had many properties, including gardens but he was not interested in learning or religion. He was an alcoholic much interested in singing and dancing. Among his gardens, he also had apple gardens. Once he took his friends to one such garden when the apples were ready to pick. There they had plenty of food and wine together with the fresh apples, and music. He himself was a good musicion and played very well. They had satiated themselves with food and were deeply intoxicated, the atmosphere was pleasant. Abdullah bin Mubarak had a guitar in his hands and he played it. He fell asleep. When he woke up, he still had the guitar in his hands. He began to play it again but it would not work. It did not produce any sound. So, he fiddled with the threads and wires and tried again but it did not omit any sound. He tried it a third time after some more fiddling with it. This time it did work but, instead of producing music, it reproduced the sound of the following verse of the Qur'an:
'Has not the time yet come for those who believe, and their hearts should be humble for the remembrance of Allah and the Truth.' (57:16)
The guitar gave out this sound. When Allah wishes to guide any of His servants then He provides such Unseen means too. The moment Abdullah bin Mubarak heard this voice, his heart accepted the Truth, and he answered the words of the verse: 'Surely, my Lord! It has arrived!'
This is the same Abdullah bin Mubarak who when visiting Baghdad during the reign of Harun al-Rashid, the Caliph heard a loud commotion from the outskirts of the city. Fearing an attack, the Caliph asked a man to find out what had happened. The man reported back that Abdullah bin Mubarak had sneezed and had said 'Praise be to Allah', and the crowd that had gathered to welcome him responded with 'May Allah have mercy on you' and the sound he had heard was of this, the crowd's response (indicating its large size and his esteemed position to attract such a crowd)."
-Mufti Taqi Usmani
(translated from oral lecture in Urdu)