Mentioned by the Holy Prophet (peace be upon him)
" Hold on to the use of the black seed for indeed it has a remedy for every disease except death"
" Hold on," indicates a long-term use - Hadith ( Sayings of the Prophet (SWS) narrated by his companions.)7.591
Narrated Khalid bin Saad (ra):
We went out and Ghalib bin Abjar was accompanying us. He fell ill on the way and when we arrived at Medina he was still sick. Ibn Abi 'Atiq came to visit him and said to us, "Treat him with black cumin. Take five or seven seeds and crush them (mix the powder with oil) and drop the resulting mixture into both nostrils, for 'Aisha (ra) has narrated to me that she heard the Prophet saying, 'This black cumin is healing for all diseases except As-Sam.' 'Aisha (ra) had asked 'What is As-Sam?' The Prophet (SWS) replied, 'Death.' " - Hadith 7.592
Narrated Abu Huraira (ra): I heard Allah's Apostle saying, "There is healing in black cumin for all diseases except death."
Salim Bin Abdullah (ra) narrates with reference to his father Hazrat Abdullah Bin Omar (ra) that Prophet Muhammad (SWS) said, "Let fall these black seeds upon you, these contain cure for all diseases except death."
The same narration is found in Sanad-e-Ahmed from Hazrat Aisha (ra) and in Ibn-al-Jozi and Trimizi from Abu Huraira (ra). Hazrat Buraida narrates that Prophet Muhammad (SWS) stated - "Shooneez is cure for all ailments except death."
It is stated in the books of seerat that Nabi-e-Akram (Pbuh) himself used to take blackseed for therapeutic purpose but with the syrup of Honey.
Khalid Bin Saad states that he was travelling with Ghalib Bin Jabr, when he fell ill during the journey. Ibn Abi Ateeq (nephew of Hazrat Aisha (ra) came to meet us. On seeing the patient, he took 5 or 7 seeds of kalonji and ground it, mixed it in olive oil and dropped in both nostrils, Hazrat Aisha (ra) told us that Prophet Muhammad (SWS) stated that there was cure in blackseed for all ailments except sam. I asked him, what was sam? He said "Death". Ghalib Bin Jabr became healthy with that treatment.