Sahih Muslim Book 26, Hadith Number 5418.

Chapter : Permission of seating a woman on the ride behind one’s back if one finds her completely exhausted in the way.

Asma’ reported: I performed the household duties of Zubair and he had a horse; I used to look after it. Nothing was more burdensome for me than looking after the horse I used to bring grass for it and looked after it, then I got a servant as Allah’s Apostle (may peace be upon him) had some prisoners of war in his possession. He gave me a female servant. She (the female servant) then began to look after the horse and thus relieved me of this burden. A person came and he said: Mother of ‘Abdullah, I am a destitute person and I intend that I should start business under the shadow of your house. I (Asma’) said: If I grant you permission, Zubair may not agree to that, so you come and make a demand of it when Zubair is also present there. He came accordingly find said: Mother of ‘Abdullah. I am a destitute person. I intend to start t mall business in the shadow of your house. I said: Is there not in Medina (any place for starting the business) except my house? Zubair said: Why is it that you prohibit the destitute man to start business here? So he started business and he (earned so much) that we sold our slave-girl to him There came Zubair to me while the money was in my lap. He said: Give this to me. I said: (I intend) to spend it as charity.