What amount of clear fluid breaks ones Wudhu?

As sallamu alaikum respected Mufti
Please advise , While performing salaah as Imam I felt a bit of moisture in my underpants I brushed the thought of as shaytaan wiswasa , after salaah I went to the bathroom and noticed a moist spot size of a grain of rice on my underpants.
Is the salaah valid or do we all have to repeat the namaaz ?
If the salaah is valid what is the amount of clear fluid that breaks the wudhu and salaah ?
Jazakallah