Abdullah bin Hammad AI-Ansari narrated from Zaid bin Osamah, who said:

كنت في جماعة من عصابتنا بحضرة سيدنا الصادق ( عليه السلام ) ، فأقبل علينا أبو عبد الله (عليه السلام) فقال : ان الله تعالى جعل تربة جدي الحسين ( عليه السلام ) شفاء من كل داء وأمانا من كل سوء وخوف ، فإذا تناولها أحدكم فليقبلها وليضعها على عينيه وليمرها على ساير جسده ، وليقل :

اللهم بحق هذه التربة وبحق من حل بها وثوى فيها وبحق أبيه وامه وأخيه والأئمة من ولده ، وبحق الملائكة الحافين به ، إلا جعلتها شفاء من كل داء وبرءا من كل مرض ، ونجاة من كل آفة ، وحرزا مما أخاف وأحذر ، ثم ليستعملها .

قال أبو اسامة : فأنا استعملتها من دهري الأطول كما قال ووصف أبو عبد الله ، فما رأيت بحمد الله مكروها

I was sitting with a group of our people (Shia) with Imam Jaafar bin Mohammad Al- Sadiq (as) when he said:

Allah, the Most Exalted, has made the dust of the grave of my grandfather, Husain (as), the cure for every disease and protection from every fear and misfortune.

When you hold the dust of his grave, kiss it, place it over your eyes, and then rub it over the rest of your body and say:

"O Allah! (I ask You) by the status of this dust, by the status of the one who is lying in it & has settled down in it, by the status of His Father, His Mother, and His Brother, by the status of the Imams from his progeny, and by the status of the angels who have surrounded His grave, to make this dust the cure for every disease, recovery from any illness. salvation from any evil, and protection from that which I fear and from which I am wary."

Zaid bin Osamah continued:

I have been using it ever since and praise be to Allah for I have not seen any misfortune.

[Source: al-Amali - Shaikh Toosi, Pg. 318]

Hasan bin Ali bin Abi Moghira narrated from Harath bin Moghira Al-Nasri, who said:

I said to Abu Abdillah, Jaafar bin Mohammad(as):

اني رجل كثير العلل والأمراض وما تركت دواء إلا تداويت به فما انتفعت به ، فقال لي : أين أنت من طين قبر الحسين بن علي (عليه السلام) ، فان فيه شفاء من كل داء وأمنا من كل خوف ، فإذا أخذته فقل هذا الكلام :

اللهم اني اسألك بحق هذه الطينة ، وبحق الملك الذي أخذها ، وبحق النبي الذي قبضها ، وبحق الوصي الذي حل فيها صل على محمد وأهل بيته وافعل بي كذا وكذا .

قال : ثم قال أبو عبد الله : أما الملك الذي قبضها فهو جبرئيل وأراها النبي (صلى الله عليه وآله) قال : هذه تربة الحسين تقتله امتك من بعدك والذي قبضها فهو محمد رسول الله وأما الذي حل فيها فهو الحسين (عليه السلام) والشهداء ، قلت : قد عرفت جعلت فداك الشفاء من كل داء فكيف الأمن من كل خوف ؟

فقال : إذا خفت سلطانا أو غير سلطان ، فلا تخرجن من منزلك إلا ومعك من طين قبر الحسين فتقول : اللهم إني أخذته من قبر وليك وابن وليك واجعله لي أمنا وحرزا لما أخاف وما لا أخاف . فانه قد يرد ما تخاف . قال الحرث بن المغيرة : فأخذت كما أمرني وقلت ما قال لي فصح جسمي وكان لي أمانا من ما خفت وما لم أخف كما قال أبو عبد الله (عليه السلام) ، فما رأيت مع ذلك بحمد الله مكروها ولا محذورا

"I am very ill. I am suffering from several diseases. I have used every kind of medicine but have not seen any result."

Imam (as) replied:

Why have you not used the clay of the grave of Husain bin Ali(as). It is the cure for every disease and it is the safety from every fear. Take the clay of his grave and say:

O Allah, I ask you through this clay, and through the right of the angel who took from it, and through the right of the Prophet who held it, and through the successor who is laying in it, to send your blessings to Mohammad and his family and ask for your needs.

Abu Abdillah(as) added:

The angel who took from it was Jibraeel who showed the land of Karbala to the Prophet(saww), saying, "This is the dust (from the grave) of Husain(as) who will be killed by your nation."

And the prophet who held it is Mohammad, the Messenger of Allah. And the successor who is laying in it is Husain, along with the rest of the martyrs.

I (Harath bin Moghira) asked, "I understood (that the dust is) a cure from disease but what do you mean by 'safety from every fear'?"

Abu Abdillah (as) replied:

If you fear a ruler or anyone else, do not leave your house unless you are carrying some of the clay of the grave of Husain(as) and say, 'O Allah! I have taken this clay from the grave of Your Wali and son of Your Wali, so make it (a guarantee of) safety and protection from that which I fear and that which I do not fear.' And you will be protected.

So I did what Abu Abdillah(as) ordered me to do. I said what he ordered me to say and my diseases were all cured. And just as he said, (the dust) was (a guarantee) of protection and safety for me from that which I feared and that which I did not fear. And I have not seen any misfortune ever since.

[Source: Amaali of Sheikh Tousi, Vol 1, Pg 325 / Kaamil al Ziyaraat, Pg 282]

محمد بن الحسن في (المصباح) بإسناده عن معاوية بن عمار قال: كان لأبي عبد الله (عليه السلام) خريطة ديباج صفراء فيها تربة أبي عبد الله (عليه السلام)، فكان إذا حضرته الصلاة صبه على سجادته وسجد عليه، ثم قال (عليه السلام): إن السجود على تربة أبي عبد الله (عليه السلام) يخرق الحجب السبع

It is narrated that Abu Abdillah Imam Sadiq (ع) had a pouch made of yellow cloth which contained the soil (Turbah) of Abu Abdillah Imam Husain (ع). So when the time for prayer (Salaat) came, He placed it on His Prayer mat and prostrated (Sajdah) on it. Imam Sadiq (ع) said, "Indeed the prostration (Sujood) upon the soil (Turbah) of Abu Abdillah Imam Husain (ع) penetrates through the seven veils."

[Source: Misbah al-Mutahajjid, Shaikh Toosi, Pg. 733]