In the Stargate episode "threads" who stops the self destruct?

It has never been explicitly said who slowed down the self destruct countdown, but for sure it wasn't Daniel Jackson. I'll be quoting some parts of this transcript of the episode.

Post climax scene in the briefing room, where Daniel himself says it wasn't him:

CARTER: I still don't quite understand what happened. One minute Anubis is about to push the button that ends all life in the galaxy, and the next minute he's just ... gone.

TEAL'C: Indeed. It is a great mystery.

BRA'TAC: One can only assume he was vanquished by some beings. If not, why would he forfeit the weapon and his army?

(Sam looks at Jack.)

CARTER: You think?

O'NEILL: I do.

CARTER: It's the only thing that would explain the self destruct not going off.

BRA'TAC: Of what do you speak?

TEAL'C: O'Neill believes that Daniel Jackson was somehow responsible.

JACKSON (offscreen): No! It wasn't me.

As to who stopped/slowed down the clock, we can only assume it was Oma (at least that's my take on it):

ANUBIS: You can't kill me either.

OMA: I can fight you.

ANUBIS: Well, you can't win.

OMA: It won't matter. You won't be able to do anything but fight me back.

ANUBIS: Well, what are you gonna do?

OMA: Something I should have done a long time ago. (She starts to walk towards him.)

ANUBIS: Oh, no. No. No! No!

(He raises his hands to try to stop her. She morphs into white light. As she reaches him, he too morphs into white light. They merge, and the light rises up and goes through the ceiling of the diner. Daniel and all the customers stare up at the ceiling. Daniel walks to the spot that they disappeared from and looks around at the customers, bewildered.)

S.G.C. CONTROL ROOM. The self destruct has reached 7 seconds. Everyone is staring around anxiously. As the self destruct reaches 1:30, the countdown starts to slow down. It takes an age to tick from 1:27 to 1:26. A couple of seconds later, the Gate shuts down.

HARRIMAN: Wormhole disengaged.

CARTER: What's going on?

HARRIMAN: I don't know. Must be some kind of ... system malfunction.

CARTER: That's impossible!

O'NEILL: Shut it off.

(Sam reaches down and types.)

CARTER: Aborting self destruct. (She finishes typing and the self destruct shuts down. She looks at Jack, who blows out a relieved breath.)

It can't be a coincidence that the clock malfunctioned at the same time Oma was fighting Anubis. Also he was only a half-ascended being, unlike Oma the full-blown Ancient, so she probably would have the power to fight Anubis and stop the self destruct. Maybe she even used the fight to hide the fact of helping less evolved beings from the other Ancients, and we all now how they feel about it...

There is no reason to assume that it wasn't another Ascended. Humans have established themselves as a force for good, the ancients are revealed to have at least a bit of respect for humans, and they are allowed to interfere in "non-direct" ways as well as if they don't know.

Further, if there is any knowledge of the future, there may be some vested interest in helping humans in general so while there is no concrete informations on who didn't do it, that fact makes points towards other Ascended.

Of course, it could also have been the Furlings ^.^

The answer is "the others". It absolutely was stated.

It is unclear what happened to Daniel after Oma attacked Anubis. Something caused the S.G.C.'s self-destruct mechanism to stop and the Stargate to disengage. Upon his return Daniel denied that he had stopped the self-destruct, implying that the Others themselves stepped in to save Stargate Command. That, and the fact that Daniel returned safely to human form -- apparently with his memory left intact -- is quite unusual for the ascended beings, who usually go out of their way to be unhelpful to "lowers." Perhaps they were swayed by Oma's selfless act in stopping Anubis.

• taken from http://www.gateworld.net/sg1/s8/818.shtml

The fact Daniel did have his memory, and made the implication that it was "the others" not himself nor Oma, I think its safe to assume Daniel Jackson's claim to be accurate.