The correct answer is: no article.
The word “little” is an indefinite adjective, which means that it does not refer to a specific person, place, thing, or amount. Indefinite adjectives do not require an article.
In this sentence, “little” is modifying the noun “information.” The sentence is saying that the amount of information he had was not quite reliable.
If we were to use an article, it would change the meaning of the sentence. For example, if we said “a little information he had was not quite reliable,” we would be saying that there was one piece of information that was not quite reliable. However, the sentence does not mean that there was one piece of information; it means that the amount of information he had was not quite reliable.
Therefore, the correct answer is: no article.