Muwatta Malik, Book 7, Hadith 28 (USC-MSA)

Malik related to me that Abd ar-Rahman ibn al-Qasim heard his father al-Qasim ibn Muhammad say, "I have prayed witr after dawn." Malik said, "Only a person who oversleeps so that he does not do the witr prays it after dawn. No one should intentionally make his witr after dawn."

وَحَدَّثَنِي مَالِكٌ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْقَاسِمِ، أَنَّهُ سَمِعَ أَبَاهُ الْقَاسِمَ بْنَ مُحَمَّدٍ، يَقُولُ إِنِّي لأُوتِرُ بَعْدَ الْفَجْرِ ‏.‏ قَالَ مَالِكٌ وَإِنَّمَا يُوتِرُ بَعْدَ الْفَجْرِ مَنْ نَامَ عَنِ الْوِتْرِ وَلاَ يَنْبَغِي لأَحَدٍ أَنْ يَتَعَمَّدَ ذَلِكَ حَتَّى يَضَعَ وِتْرَهُ بَعْدَ الْفَجْرِ ‏.‏

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also referenced under: Book 7, Hadith 282 (In-Book)