I'm starting in Wikipedia, where "clinging to rites and rituals" is defined as one of the "fetters". This answer assumes that "clinging to rites and rituals" is (the same as) the "superstition" you were asking about, and so this answer will give references to describe what "clinging to rites and rituals" means.
From Wikipedia, Fetter (Buddhism), the third fetter is,
- attachment to rites and rituals (sīlabbata-parāmāsa)
Attachment to rites and rituals (sīlabbata-parāmāso)
Śīla refers to "moral conduct", vata (or bata) to "religious duty, observance, rite, practice, custom," and parāmāsa to "being attached to" or "a contagion" and has the connotation of "mishandling" the Dhamma. Altogether, sīlabbata-parāmāso has been translated as "the contagion of mere rule and ritual, the infatuation of good works, the delusion that they suffice" or, more simply, "fall[ing] back on attachment to precepts and rules."
Wikipedia then gives the following paragraph which may or may not be helpful -- on the one hand it's relevant to the conventional meaning on superstition, but on the other hand Thanissaro Bhikkhu's description of it below says it has a broader meaning (e.g. that merely clinging to even Buddhist precepts isn't right):
While the fetter of doubt can be seen as pertaining to the teachings of competing samana during the times of the Buddha, this fetter regarding rites and rituals likely refers to some practices of contemporary brahmanic authorities.
A footnote mentions "the similar concept of sīlabbatupādāna (= sīlabbata-upādāna), 'grasping after works and rites.'"
From Wikipedia's Sotāpanna article,
- Clinging to rites and rituals - Eradication of the view that one becomes pure simply through performing rituals (animal sacrifices, ablutions, chanting, etc.) or adhering to rigid moralism or relying on a god for non-causal delivery (issara nimmāna). Rites and rituals now function more to obscure, than to support the right view of the sotāpanna's now opened dharma eye. The sotāpanna realizes that deliverance can be won only through the practice of the Noble Eightfold Path. It is the elimination of the notion that there are miracles, or shortcuts.
Following Wikipedia's footnoted references to the suttas, one is Lohicco Sutta which says that Brahmans have their rituals (garbs of skin, chanting, ritual washing), but that these actions aren't right.
First in virtue were the men of old,
Brahmans who preserved the ancient ways,
In whom well guarded were the doors of the sense.
They were never overcome by wrath.
Meditating on the Law their joy,
Brahmans who preserved the ancient ways.
These backsliders who but chant by rote,
Drunk with pride of birth they stagger on.
Full of violent rage, aggression prone,
They lose respect from weak and strong alike:
Their unguarded senses bring them loss,
Like a treasure hoard found in a dream.
Fasting, sleeping on the ground, and such,
Dawn ablutions, chanting Vedic texts,
Garb of skins, matted hair and filth,
Magic spells and rites and penances,
Trickery, deception, blows as well,
Ritual washing, rinsing of the mouth,
These are caste-marks of the Brahman-folk,
Done and practiced for some trifling gain.
But a heart that's firm and concentrated,
Purified, of all defilements freed,
Kind and gentle to all living things-
That's the path that gains the highest goal.
Another description of this fetter is in Thanissaro Bhikkhu's Into the Stream
A Study Guide on the First Stage of Awakening,
The fetter of grasping at habits and practices is often described in the Pali Canon with reference to the view that one becomes pure simply through performing rituals or patterns of behavior. This view in turn is related to the notion that one's being is defined by one's actions: If one acts in accordance with clearly defined habits and practices, one is ipso facto pure. Although the Canon recognizes the importance of habits and practices in the attaining the stream, the experience of the Deathless shows the person who has attained the stream that one cannot define oneself in terms of those habits and practices. Thus one continues to follow virtuous practices, but without defining oneself in terms of them.
"Now where do skillful habits cease without trace? Their cessation, too, has been stated: There is the case where a monk is virtuous, but not fashioned of (or: defined by his) virtue. He discerns, as it actually is, the awareness-release & discernment-release where his skillful habits cease without trace."
— MN 78
[The enlightened person] doesn't speak of purity
in terms of view,
habit or practice.
Nor is it found by a person
through lack of view,
of habit or practice.
Letting these go, without grasping,
one is independent,
— Sn 4.9
The first of these two referenced suttas, Samana-Mundika Sutta (MN 78) says that doing no wrong isn't enough -- that merely doing no wrong is "on the same level as a stupid baby boy lying on its back" -- that person needs skillful resolves and habits, and (as quoted above) discernment of cessation.
The last reference Magandiya Sutta (Sn 4.9) is more on the subject of not clinging, of not being fashioned by views, not being led by actions, not being tied by perception (of better and worse).