Sahih al-Bukhari Book 48, Hadith 4
The Prophet (ﷺ) said, "One can ride the mortgaged animal because of what one spends on it, and one can
drink the milk of a milch animal as long as it is mortgaged. "
Allah's Messenger (ﷺ) said, "Who would kill Ka`b bin Al-Ashraf as he has harmed Allah and His Apostle ?" Muhammad bin Maslama (got up and) said, "I will kill him." So, Muhammad bin Maslama went to Ka`b and said, "I want a loan of one or two Wasqs of food grains." Ka`b said, "Mortgage your women to me." Muhammad bin Maslama said, "How can we mortgage our women, and you are the most handsome among the Arabs?" He said, "Then mortgage your sons to me." Muhammad said, "How can we mortgage our sons, as the people will abuse them for being mortgaged for one or two Wasqs of food grains? It is shameful for us. But we will mortgage our arms to you." So, Muhammad bin Maslama promised him that he would come to him next time. They (Muhammad bin Maslama and his companions came to him as promised and murdered him. Then they went to the Prophet (ﷺ) and told him about it.
Allah's Messenger (ﷺ) said, "The mortgaged animal can be used for riding as long as it is fed and the milk of the milch animal can be drunk according to what one spend on it. The one who rides the animal or drinks its milk should provide the expenditures."