What's the origin of 108 being a sacred number? The number 108 is a sacred number in Buddhism, but in other religions as well (Hinduism, Jainism). 
What exactly is the origin of 108 being a sacred number in Buddhism? Is there anything about it in the ancient scriptures? Did the Buddha say anything about it? Or is it more likely that this was incorporated from other older beliefs?
The origin of 108 in the ancient buddhist scriptures seems to be from the total number of feelings classified in different ways by the Buddha:

&quot;Monks, I will teach you a one-hundred-and-eight exposition that is a
Dhamma exposition. Listen &amp; pay close attention. I will speak.&quot;
&quot;As you say, lord,&quot; the monks responded.
The Blessed One said: &quot;And which one-hundred-and-eight exposition is a
Dhamma exposition? There is the exposition whereby I have spoken of
two feelings, the exposition whereby I have spoken of three
feelings... five... six... eighteen... thirty-six... one hundred and
eight feelings.
&quot;And which are the two feelings? Physical &amp; mental. These are the two
feelings.
&quot;And which are the three feelings? A feeling of pleasure, a feeling of
pain, a feeling of neither pleasure nor pain. These are the three
feelings.
&quot;And which are the five feelings? The pleasure-faculty, the
pain-faculty, the happiness-faculty, the distress-faculty, the
equanimity-faculty. These are the five feelings.
&quot;And which are the six feelings? A feeling born of eye-contact, a
feeling born of ear-contact... nose-contact... tongue-contact...
body-contact... intellect-contact. These are the six feelings.
&quot;And which are the eighteen feelings? Six happiness-explorations, six
distress-explorations, six equanimity-explorations. These are the
eighteen feelings.
&quot;And which are the thirty-six feelings? Six kinds of household
happiness &amp; six kinds of renunciation happiness; six kinds of
household distress &amp; six kinds of renunciation distress; six kinds of
household equanimity &amp; six kinds of renunciation equanimity. These are
the thirty-six feelings.
&quot;And which are the one hundred and eight feelings? Thirty-six past
feelings, thirty-six future feelings, and thirty-six present feelings.
These are the one hundred and eight feelings.
&quot;And this, monks, is the one-hundred-and-eight exposition that is a
Dhamma exposition.&quot;
-SN 36.22, Discourse on One-hundred-and-eight (Aṭṭhasatasuttaṃ)

There is also a reference to 108 Craving-verbalizations in AN 4.199, Discourse on Craving (Taṇhā-suttaṃ).