Is the emission of pre-seminal fluid (madhy) after an erection, without deliberate thought, considered unlawful (haram)? And is it permissible to purify a garment that has been sprinkled with it by using water?

There is no sin on someone from whom pre-seminal fluid (madhy) is discharged due to thoughts, but one should guard against intrusive thoughts and avoid anything that incites lust. It is obligatory to perform istinja' (washing the private parts) from madhy and wash any part of the body that it has touched. As for clothes, it is sufficient to sprinkle water on the part that it has soiled.