The Book of Fasting
وَحَدَّثَنِيهِ يَعْقُوبُ الدَّوْرَقِيُّ، حَدَّثَنَا إِسْمَاعِيلُ، عَنِ ابْنِ عَوْنٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، وَمَسْرُوقٍ أَنَّهُمَا دَخَلاَ عَلَى أُمِّ الْمُؤْمِنِينَ يَسْأَلاَنِهَا . فَذَكَرَ نَحْوَهُ .It is further narrated on the authority of Aswad and Masruq that they went to the Mother of the Believers and they asked her (and the rest of the hadith is the same)
From Sahih Muslim, whose reports the scholars accept as authentic.