Shamelessly stolen from somewhere else:
86 is meant to be the number of 'bismillahirahmaniraheem (In the name of Allah, the Beneficent, the Merciful - which is the first verse of the Quraan)
In arabic, each letter has a number
alif -1
bee 2
etc
if you add the numbers up, for bismillah in arabic, you get 786.
That is where the number came from.
However, someone else then says:
Firstly, 786 - does not mean 'bismillahirahmaniraheem:.
Numerology is an old age science, its origins are from paganism rituals, dating as far back as the Greeks, it is nothing new. The system that has been used to come up with the 786 number is called Abjad system of numerology and is used among muslim mainly in the sub-continent and comes from the Jewish cablist system called gematria..
Also those of you from Indian origin should know the hindu’s use 786 as well, this for them this means Hari Krishna .