Well, there could be a few issues going on here. We need to know more about the circumstances to better understand the situation.  Is the sample a soundpool object?  HOW do you know the tempo?  Is there an actual tempo assigned to the sample?

If there is a tempo already assigned to the sample, and it is imported into an arrangement with a different tempo, the sample tempo will usually be altered to match the arrangement tempo.  To prevent this, you must turn off the tempo adaptation feature in the Program Settings.

Program Settings ('Y' key) > Import (tab) > Automatically adjust samples to BPM (timestretch)

Please note:

The default arrangement tempo is 120 BPM.  You can change this to any tempo you desire, HOWEVER if the first object you import has a different tempo assigned to it, the arrangement tempo will automatically change to match it.

So, if you want to create an arrangement at a tempo to match a specific sample, that sample must be the first one imported into the arrangement.

An altenative is to first set the arrangement tempo as desired and then open a beatbox object in the arrangement.  This way, the tempo you want will be "locked in" as the arrangement tempo.  Then, all other tempo assigned soundpool objects and samples will be altered to match the desired arrangement tempo.  That is unless you've turned off the tempo adaptation feature.

Beyond that, you can alter the tempo of any individual object (sample) using the Time Processor feature in the Object Effects Rack.