phil wrote:"When the mind is disturbed it is far from concentration." (MN 19 or 20, I think, but don't count on it, but it is the Buddha's teaching.)
"api ca kho me aticiraṃ anuvitakkayato anuvicārayato kāyo kilameyya . kāye kilante cittaṃ ūhaññeyya. ūhate citte ārā cittaṃ samādhimhāti."
"And so, indeed, when I was investigating and reflecting for a long time, the body would become tired. When the body was tired, the mind would be disturbed. When the mind is disturbed, the mind is far from concentration."
-- MN 19
Not really proof that concentration cannot be accompanied by unwholesomeness....
In another sutta it is said that guarding the sense doors and sila lead to freedom from remorse, and that is a condition for samadhi.
I believe this was discussed already, but I think the concentration implied here is right concentration, and the wording is that freedom from remorse is for the purpose of concentration (I think actually there are a few more links here...). So at best it is a support, but not a necessary condition.
Other people will tell you that (according to Abhidhamma) concentration is a cetasika that accompanies every citta and that right samadhi can occur with any object at any time, but I think that is their very self-generous wishful thinking.
It is one thing to say that concentration is a cetasika, it is another to say that right samadhi can occur with any object at any time. Since it does actually say that samadhi is a universal cetasika in the abhidhamma, it might just be because they respect the authority of that body of texts that they tell you that. And since it does seem to be supported by scientific inquiry, why be dogmatic in refusing to admit it? According to both the sutta and the abhidhamma, there is something called micchāsamādhi, as pointed out above. It is quite obvious that micchāsamādhi is accompanied by unwholesomeness, so obviously the two can go together. There is no reason to think that micchāsamādhi does not exist at the moment of committing an offence against one's sīla.
Personally, my practice is all about establishing sila, I personally think aspiring for right samadhi without sila is an absurdity, and I say that both from watching the mind, and from the Buddha's teaching, as above.
I may be wrong, but I think the OP was asking about samādhi in general, not only sammāsamādhi, which everyone should agree cannot come without concurrent sammāsīla.
Wrong concentration is focussing the mind on a misdeed that one intends to commit by body or speech. It is concentration that enables one to do unwholesome deeds successfully. For example, when you intend to tell a lie, your intention will materialise only if you fix your mind on the words that you have to utter falsely. If your mind wanders, you are likely to speak the truth unwittingly. It is said that in courts the truth about some cases comes to light when witnesses who have agreed to give false evidence are tricked by lawyers whose cross-examination is designed to create confusion. This is due to lack of concentration on the part of the witnesses, so concentration is vital when doing an evil deed. Wrong concentration is very powerful when men plan a massacre, a big robbery, or produce lethal weapons.
-- Mahasi Sayadaw, Sallekha Sutta