It is narrated from Hazrat Abu Rafi' (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) forbade men from tying their hair in knots while performing prayer.
Hadith Referenceمسند احمد / من مسند القبائل / 27184
Hadith Gradingحکم دارالسلام:صحيح لغيره، وقد اختلف فى تعيين الرجل المبهم، واختلف فى إسناده على مخول