circumference of the inner palm

Q: Can we say zikr and salat if we have najaasat (e.g. small amount of urine) on our clothes or body?

Q: I performed Salaah not knowing that there was mazi on my clothes. It was only a few hours after performing the Salaah that I realized that my clothes has been soiled. Is that Salaah valid or do I have to repeat it?