Narrated Abu 'Is-haq:
A man asked Al-Aswad, 'is it 'Fahal min-Muddakir' or'..Mudhdhakir?" Al Aswad replied, 'I have heard `Abdullah bin Masud reciting it, 'Fahal-min Muddakir'; I too, heard the Prophet (ﷺ) reciting it 'Fahal-min-Muddakir' with 'd'.
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 394
Arabic reference: Book 65, Hadith 4871