Musnad Ahmad 32:338

'Abd al-Samad narrated to us, 'Ubayd Allah ibn Shumayt narrated to us, he said: I heard 'Abd Allah al-Hanafi narrating that he heard Anas ibn Malik, from the Prophet, may Allah bless him and grant him peace, that he said: "Indeed, begging is not permissible except for three: for one who possesses abject poverty, or for one who possesses a crushing debt, or for one who possesses a painful blood-wit."