Learn Farsi: روی تخت نپر. - Do not jump on the bed.

To make a negative command, you add the prefix نـ (na-) to the present stem of a verb. The verb for "to jump" is پریدن (paridan), and its present stem is پر (par). Combining them gives you نپر (napar), meaning "don't jump".

Why doesn't نپر have a personal ending?

When giving a command to one person informally, you drop the personal ending completely. You only use the prefix and the stem. If you were speaking formally or to multiple people, you would add the -id ending to make it نپرید (naparid).

Why is it pronounced روی (ru-ye) instead of just "ru"?

The word for "on" is رو (ru). When linking a preposition like this to a noun like تخت (bed), Farsi uses a linking vowel called the ezāfe. Because رو ends in a vowel, the ezāfe is pronounced as a "ye" sound to make it flow smoothly, giving us روی تخت (ru-ye takht).