It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that "the Messenger of Allah (peace and blessings be upon him) forbade a man to pray while the hair of his head is tied up or knotted into a bun (at the back)."
(Imam Ishaq said:) I asked al-Mu'ammal whether Sayyidah Umm Salamah (may Allah be pleased with her) is mentioned in the chain of this narration. He replied: I have no doubt at all about it; I first wrote it down from him in this way in Makkah. I (Ibn Hajar) say: Abd al-Razzaq and Waki' also narrated this hadith from Sufyan al-Thawri, but in their narration Sayyidah Umm Salamah (may Allah be pleased with her) is not mentioned; Imam Ahmad (may Allah have mercy on him) recorded it in his book through these two teachers, and it was because of this discrepancy that Ishaq sought confirmation of it again from al-Mu'ammal. So if al-Mu'ammal preserved it correctly, then this discrepancy lies within Sufyan's own narration (in that he sometimes narrated it from Umm Salamah and sometimes without her), and is not an objection against him. And Allah knows best.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الصلاة / 388
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :الحديث بهذا الإسناد رجاله كلهم ثقات، إلا مؤمل بن إسماعيل فإنه صدوق يخطئ كثيرا. » «أخرجه مسند أحمد برقم: 23344، وأخرجه المعجم الكبير للطبراني برقم: 990، وأخرجه مجمع الزوائد ومنبع الفوائد برقم: 2469»