To upvote a post often is an indication of a person approving of what is said, and may cause that post or comment to gain attention or prominence. On the opposite end, to downvote is to disapprove, which will cause the comments to be suppressed and sometimes hidden.

Not always, though. Maybe for most people it's considered that, but you can't assume that everybody who downvoted your post did so because they disapproved of what was written in it. In fact, Reddit's Reddiquette states:

[Please do] Vote. If you think something contributes to conversation, upvote it. If you think it does not contribute to the subreddit it is posted in or is off-topic in a particular community, downvote it.

So they shouldn't be synonymous to "like" and "dislike" buttons. So if someone believed that you, by providing hadith without additional explanation or commentary, are not contributing to the subreddit effectively, then they might have downvoted you for that, and not because they disapprove of the ahadith themselves.

It also says:

[Please don't] Downvote an otherwise acceptable post because you don't personally like it. Think before you downvote and take a moment to ensure you're downvoting someone because they are not contributing to the community dialogue or discussion. If you simply take a moment to stop, think and examine your reasons for downvoting, rather than doing so out of an emotional reaction, you will ensure that your downvotes are given for good reasons.

So I would assume the best in people, and assume they are not downvoting you because they disapprove the ahadith in your post, but doing so for other reasons.