It is narrated from Sayyidah Sumaytah (may Allah be pleased with her), a woman of Banu Layth bin Bakr who was raised in the care of the Messenger of Allah (peace and blessings be upon him). The narrator said: I heard her relating to Safiyyah bint Abi Ubayd that she heard the Prophet (peace and blessings be upon him) say: "Whoever among you is able to die in Madinah, let him die there, for he will die a martyr, and intercession will be made for him."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21194