Musnad Ahmad 949:15

Bahz narrated to us, Hammad narrated to us, Sa'id ibn Jumhan informed us, Safinah narrated to me: A man was a guest of Ali, so he prepared food for him. Fatimah said to Ali: "If only you would invite the Prophet, may Allah bless him and grant him peace, so he could eat with us." So we invited him, and he came and took hold of the two doorposts. We had hung a decorated curtain in a corner of the house. When he saw it, he turned back. Fatimah said to Ali: "Follow him and see what made him turn back." He said: "What turned you back, O Prophet of Allah?" He said: "It is not for a prophet to enter a decorated house."