A colleague just asked me which dining halls were open. I pasted text from the Dining Services website into an email in response, without quotation marks or other indication of quotation. (In an academic context, the lack of quotation marks would make it plagiarism, but not in this very informal context.) The text I pasted into the email constituted assertions whose content I did not believe, simply because by the time I pasted it, I had forgotten what it said (I have no memory for times and the like). But I believed, maybe even knew, that the assertions were all true, and there was no dishonesty.
In a similar way, it is possible to assert something you know to be true, and yet be lying. Suppose I am writing my chair to convince him of some point of policy and I have an unscrupulous colleague who emails me a complex sentence that he says is false but will convince the chair. I trust the savvy of my unscrupulous colleague and paste the sentence into my email without bothering to read it. It turns out that my unscrupulous colleague was mistaken, and the sentence is true, and in fact it expresses a truth that I believe. I then send the email to the chair. In so doing, it seems that I lied to the chair, even though I asserted something which I knew to be the case.
One might think that this isn't lying. If it's not, it's something morally equivalent to it, and our category of "lying" is artificially constricted.