Question Summary:
Do I need to wash my underpants for namaaz if soaked with mazi?

Question Detail:

If my outerpant also got little wet because of thin underwear due to mazi drops.Does I wash outerpant before salah. Answer me please

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Mazi is Najasat e Ghalizah.[1] In principle, If clothes are soiled with Madhi which is equal or less than the hollow of your palm (which approximately has a diameter of 2.75cm) then Salah in such clothes will be valid but Makrooh-e-Tanzīhī (undesirable). If it is more than the hollow of your palm, then to read Salaah with such clothes will be Makrooh-e-T6ahrimi (reprehensible). [2]
 
Therefore, If you know from beforehand that there is Madhi on your underpants
lesser than 2.75cm diameter, then it will be Afdhal (better) for you to wash it. However, if you fear that you will miss your Jama῾ah if you take time to wash it, then you should continue with the Jama῾ah. If the underpants has soiled more than 2.75cm diameter, then you will have to wash that portion before performing your salaah, even if in doing so you miss your Jama῾ah.[3] This ruling is for both, underpants and outer pants.