Is it possible for a Muggle-born to be sorted to Slytherin? We know that half-bloods can like Snape and Voldemort, but how about Muggle-borns?
If it is possible, was there an example from canon to prove this?
In the last book, one of the snatchers mentions that there aren't a lot of Slytherin mudbloods, which indicates there could be few muggle born Slytherins:
"Well, well, looks like we really 'ave caught a little Slytherin." said Scabior. "Good for you, Vernon, 'cause there ain't a lot of Mudblood Slytherins. Who's your father?"
Also, I was able to dig this up, but I don't have much ideas about it's validity. But if it is true, then these Slytherin students are apparently muggleborns:
I will try to find out more if possible and update it later. If someone knows for sure that this is fake, please mention it in the comments, with a link for proof.
I'm thinking this passage might refer to Dean Thomas:
‘Well, well, looks like we really ’ave caught a little Slytherin,’ said Scabior. ‘Good for you, Vernon, ’cause there ain’t a lot of Mudblood Slytherins. Who’s your father?’
Deathly Hallows - page 365 - Bloomsbury - chapter twenty-three, Malfoy Manor
I thought of Dean when Greyback says this:
‘Not a bad little haul for one night,’ Greyback was saying, as a pair of hobnailed boots marched close by Harry and they heard more crashes from inside the tent. A Mudblood, a runaway goblin and three truants. You checked their names on the list yet, Scabior?’ he roared.
Deathly Hallows - page 364 - Bloomsbury - chapter twenty-three, Malfoy Manor
The Muggleborn could be Dean Thomas, who was captured at the same time the trio was. The Goblin is obviously Griphook. The three truants might be Harry, Ron, and Hermione. Or Greyback could be referring to Harry as the Slytherin Muggleborn, even though Harry never discloses his blood status to Scabior and Greyback. Food for thought.
Despite Greyback's comment on finding a "Mudblood Slytherin" (Which really does indicate when he says "a Mudblood" to Scabior, he is talking about Harry, because Harry was able to both tell the Snatchers where the Slytherin common room was, but was also able to describe the inside of the common room.) is challenged by the welcome letter for Slytherin House from Pottermore, which suggests there are purebloods and half-bloods in Slytherin:
Please do not convert the image to text; I want people to know it's from Pottermore. Unfortunately, you can't link directly to the page with the image of the welcome letter.
"At least one Muggle parent" leaves open the possibility that there could be Slytherin students who have two Muggle parents.
Canon makes no reference to any Muggleborn students in Slytherin, at least not specifically, and I can't recall an interview with J.K. Rowling where she names any Muggleborn Slytherin students.
Sorry this might be long, and I'll be refering to the same quote that's already been used, but I understood it differently:
While in hiding, Harry broke the Taboo and he, Hermione and Ron were taken by Snatchers. These were looking for "undesirables", Muggle-borns, under-age not in Hogwarts aso...
Hermione modified Harry's face, and he told his name was Vernon Dudley. This name was not on the list of "wanted people" (to the contrary of Potter, or Granger, or Muggle-borns who didn't register at the Ministry, or Order's members...).
But the Snatchers wanted to be sure this was not a cover name. So they asked Harry what his house was. He said Slytherin, and, since he could describe Slytherin's common room, they believed him.
And from that moment on, they accept that he's not a Muggle-born on the run. Cause for them, being a Slytherin is not compatible with being a Muggle-born.
You checked their names on the list yet, Scabior?” he roared.
“Yeah. There’s no Vernon Dudley un ’ere, Greyback.”
“Interesting,” said Greyback. “That’s interesting.”
“So you aren’t wanted, then, Vernon? Or are you on that list under a different name? What house were you in at Hogwarts?”
“Slytherin,” said Harry automatically.
“Funny ’ow they all thinks we wants to ’ear that.” leered Scabior out of the shadows. “But none of ’em can tell us where the common room is.”
“It’s in the dungeons.” said Harry clearly. “You enter through the wall. It’s full of skulls and stuff and its under the lake, so the light’s all green.”
There was a short pause.
“Well, well, looks like we really ’ave caught a little Slytherin.” said Scabior.
“Good for you, Vernon, ’cause there ain’t a lot of Mudblood Slytherins.
(Deathly Hallows, Chapter 23, Malfoy Mannor)
If you've still got a doubt, let's see what comes next:
They ask Harry (Vernon to their eyes) what his father does. He says he works at the Ministry, and one of the Snatchers recalls of a Mr. Dudley working there. This is for them the final confirmation that he's saying the truth (ahem).
"Who’s your father?”
“He works at the Ministry,” Harry lied. [...] “Department of Magical Accidents and Catastrophes.”
“You know what, Greyback,” said Scabior. “I think there is a Dudley in there.”
Harry could barely breathe: Could luck, sheer luck, get them safely out of this?
“Well, well.” said Greyback, and Harry could hear the tiniest note of trepidation in that callous voice, and knew that Greyback was wondering whether he had just indeed just attacked and bound the son of a Ministry Official.
(Deathly Hallows, Chapter 23, Malfoy Mannor)
They wouldn't have asked someone they took for a Muggle-born who was his father. And they wouldn't have accepted "he works for the Ministry of Magic" as an answer.
So what I read there is that for the Snatchers, being a Slytherin is as good as a proof you're not a Muggle-born.
This added to the reputation of Salazar Slytherin's refusing to teach Muggle-borns (remember he is the guy who hid a Basilisk in the school he co-founded, just to "purify" it from Muggle-borns...) will have me say that
(and by the way, which Muggle-born would want to be sent to Slytherin anyway?)
The Sorting Hat sang about the history of the Hogwarts house
Said Slytherin, "We'll teach just those
Whose ancestry's purest."
For instance, Slytherin
Took only pure-blood wizards
Of great cunning just like him.
Though the hat may have adapted the original criteria.
As far as I know there are no examples in canon, but in DH one of the snatchers states that there are very few (not zero) Muggle-borns in Slytherin.
Salazar Slytherin DID say to the sorting hat to not put MUGGLE-BORNS, but there are no proof that he also say that only PURE-BLOODS can be in Slytherin, so that explains why SEVERUS SNAPE and TOM RIDDDLE is in slytherin while their parents are a witch and muggle father
Well there were muggle borns in Slytherin like Millicent Bulstrode and Amelaie Greengrass. I think there were more, but in Rowling's original notes that she put in public, these were the only ones I could find.
When Scabior said that there aren't a lot of mud bloods in Slytherin, he said it 100% sarcastically. Which means that there aren't Slytherin muggle borns at all! Bulstrode, Millicent was actually a half-blood NOT muggle born. (And yes, half-bloods are allowed in Slytherin BTW) Rowena, Helga, Godric and Salazar put their requirements for the students that are going to be in their house, there is a high chance that one of the requirements of Salazar Slytherin was NO MUGGLE-BORNS as he thought that muggle borns didn't deserve to learn magic. This is what I think, according to my research.