Jisho

It's not wrong, it's just contextless. のだから is generally a conector between the two sentences, but in this case the second sentence (the thing being explained) is implied in context. For example consider this possible conversation:
「なんでそんなに汗びっしょりなの？」 "Why is/are [pronoun] so sweaty?" (this sentence can be talking about you, he, she, it, they, depending on context)
「１日中テニスをしていたんだから。」"(Because) [pronoun] was playing tennis all day"
Here I shortened のだから into んだから, because that's a more conversational form (it's still the same thing).
When you see だから or other particles at the end of a sentence that is being treated as complete, that means the rest of the sentence is already clear in context or the person wants you to infer.

Thank you！