Muwatta Malik, Book 7, Hadith 279 (In-Book) ⓘ
Yahya related to me from Malik from Hisham ibn Urwa from his father that Abdullah ibn Masud said, "I do not mind if the iqama for the subh prayer is called while I am still praying witr."
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، قَالَ مَا أُبَالِي لَوْ أُقِيمَتْ صَلاَةُ الصُّبْحِ وَأَنَا أُوتِرُ، .
also referenced under: Book 7, Hadith 25 (USC-MSA)