In Tehillim 23, David says "Even when I walk in the valley of darkness, I will fear no evil for You are with me". Someone asked me if this "valley of darkness" is metaphorical or physical and, either way, what it refers to more specifically. I consulted Rashi on Tehillim 23:4, who says:
in the valley of darkness: Heb. צלמות, in a land of darkness. He alludes to the desert of Ziph (I Sam. 23:13 28). Every [mention of] צלמות is an expression of darkness. Dunash ben Labrat defined it [in this manner].
I Samuel does talk about the desert of Ziph (23:24). But according to Strong's concordance (Christian web site, only concordance I could find online) the word צלמות occurs several other times in Tehillim too: 44:20 ("you covered us with darkness"), 107:10 ("Those who sit in darkness and the shadow of death, prisoners of affliction and iron"; Rashi compares to people in dungeons), 107:14 ("He took them out of darkness and the shadow of death"). Those other uses of the word appear to be more general, not referring to particular events.
The other psalms that use this phrase, and 23 otherwise, seem to be more general praise of God. If 23 does allude to a specific event as Rashi says, where do we learn this?