Faqeeh Abu Muhammed Ishbeeli (rahimahullah) has recorded the following incident in his kitaab on the virtues of haj:
Once, a man from the city of Granada became so ill that the doctors were unable to treat him and gave up hope of his recovery. At that time, the governor, Abu ‘Abdillah, Muhammed bin Abil Khisaal, wrote a letter addressed to Rasulullah (sallallahu ‘alaihi wasallam) which he gave to the Haajis to be read at the blessed grave of Rasulullah (sallallahu ‘alaihi wasallam). In the letter, the governor also included some verses of poetry.
When the caravan of riders arrived in Madinah Munawwarah and this letter, with the poetry, was recited at the grave of Rasulullah (sallallahu ‘alaihi wasallam), then the sick man was instantly cured by Allah Ta‘ala while at home in Granada.
Hence, when the Haajis later returned to Granada, they found that the man had made such a complete recovery that it seemed as though he had never been ill.
(Wafaa-ul-Wafaa 4/204-205)