Sayyiduna Abu Shaqrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When you see those women who make on their heads (by tying up their hair) a bun like the humps of cattle, then inform them that their prayer is not accepted."
Hadith Referenceالمعجم الكبير للطبراني / مسند من يعرف بالكنى / 19131