Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1797
Abu Ishaq reported: I saw a man asking Aswad b. Yazid who taught the Qur'an in the mosque: How do you recite the verse (fahal min muddakir) whether (the word muddakir) Is with (d) or (dh)? He (Aswad) said: It was with (d). I heard Abdullah b. Mas'ud saying that he had heard the Messenger of Allah (may peace be upon him) reciting (muddakir) with (d).