I want to offer reliable sources (as asked for) for both the equity as well as commonly understood differences between ethics and morals. Please keep in mind that some authors do define their usage completely different.
Your first task in philosophy is always to understand the usage of the terminology in the particular text you read. Or, respectively, carefully making your own understandings explicit by delivering definitions.
Ethics = morals
First, the distinction between ethics and morals is to some extend artificial and did, to my knowledge, not occur before the Enlightenment. As Virmaior rightfully stated, they were in the beginning just two words with the very same meaning, where moral(s) has simply been the latin translation of greek ethics:
The term ethics derives from the Ancient Greek word ἠθικός ethikos, which is derived from the word ἦθος ethos (habit, "custom"). Source
[moral] literally "pertaining to manners," coined by Cicero ("De Fato," II.i) to translate Greek ethikos (see ethics) from Latin mos (genitive moris) "one's disposition," in plural, "mores, customs, manners, morals," a word of uncertain origin. Source
As you can see, both simply meant ‘customs’, or (social) ‘habits’. Therefore, there are good reasons to state in the introduction to Copp, David (Ed.) (2007). The Oxford Handbook of Ethical Theory. Oxford: Oxford University Press.:
It is worth saying at the outset, moreover, that in this volume, “morality” and “ethics” are used interchangeably. (p.4)
Ethics and morals as distinct
Nevertheless, the very same introduction seems to suggest three different meanings or 'layers of reflection' of ethics/morals at the same time. The first one seems to me, though not explicitly stated, ethics in a narrower sense of simply living a (good) life or living according to (social) customs/habits. It is implicitly stated in the description of its 'meta-level', the (philosophy of) morals:
Moral philosophy addresses the many abstract ethical and philosophical issues that arise when we attempt to make such decisions [i.e. regarding controversial social issues] in a reflective and responsible way. (p.4)
I read it as follows: a) There may occur ‘controversial social issues’. b) These issues may raise or reveal issues in the social customs/habits, i.e. in ethics. c) When these issues are addressed ‘in a reflective and responsible way’ (probably: abstract/general considerations?), we speak about morals, i.e. a field in that ethics is reflected upon.
Now, we can reflect on morals, i.e. our way of reflecting upon social issues, as well:
It requires making a claim about moral claims or about morality. This explains why the issues in this category are called “second-order” or “metaethical.” (p.5)
As the Oxford Handbooks are always a good start, I would go with it.
Aside: Kant on this distinction
Kant introduces a clear distinction (as also stated by Virmaior) in his Metaphysics of Morals:
In ancient times “ethics” signifıed the doctrine of morals [Sittenlehre, can also be translated to doctrine of customs]; (philosophia
moralis) in general, which was also called the doctrine of duties . Later on
it seemed better to reserve the name “ethics” for one part of moral
philosophy, namely for the doctrine of those duties that do not come
under external laws (it was thought appropriate to call this, in German, the doctrine of virtue [Tugendlehre]). Accordingly, the system of the doctrine of
duties in general is now divided into the system of the doctrine of Right
(ius), which deals with duties that can be given by external laws, and
the system of the doctrine of virtue (ethica), which treats of duties that
cannot be so given; and this division may stand. (Ak. 6:379.3-12)
That means that for Kant, everything that can be enforced by society through law belongs to morals, whereas all other duties (of a fair and just life that fullfils the full notion of a finite rational being that humans are) belong to ethics.
This can be neatly intertwined with the considerations offered above, as laws for Kant are in the first place general rules in the strict sense (i.e. do not allow for exceptions). This means they include general/abstract considerations on socially relevant habits/customs, as they define and influence them.