Hadith on Recommendation of Fasting on first Muharram
Rāyyan bin Shabeeb (the maternal uncle of Mo'tasim), says that I went to meet Imām Ali ar Rezā (a.s.) on the First day of the month of MuharramImām Alī ibn Mūsā al-Rezā (A.S.) asked:"“O son of Shabeeb! Are you in the state of fasting today”?
I (Rāyyan bin Shabeeb) replied in the negative. Imām (a.s.) continued,“This is the day when Prophet Zakariyyah (a.s.) prayed to his Lord thus:“Lord grant me from unto Thee a good offspring, Verily Thou art the Hearer of Prayers” (Surah al-Ali Imran, 3:38).Then Allāh (s.w.t.) accepted his Prayers and commanded His Angels to go and give him glad tidings regarding the birth of his son Prophet Yahyā (a.s.). The Angels came and called out to him while he was engaged in Prayers in the niche. Hence the one who fasts on this day and asks for his desires from Allāh, his Prayer will be answered as was of Zakariyāh.”
[References: Nafasul Mahmum, Chapter 3, Section 2, Tradition 1]
Sayyid Ibn Tawus has mentioned the merits of observing fasting during the whole month of Muharram adding that such a deed protects against committing any sin.
Take a Ghusl /bath,
with the intention(Niyat) of "Rija" for cure/protection from illness .Recite the following Dua on the water to be used:-
Subh'anallahi maal-al mizaan Subh'anallahi muntahal h'ilm
Glory be to Allah the Supreme balance ,Glory be to Allah the Ultimate in gentleness,

Subh'anallahi mublaghar riz'aa Subhanallahi zinatal a'rsh

Glory be to Allah the Goal of devotedness, Glory be to Allah the splendor of the Arsh