Wa'alaikumussalam! Untuk stain yang dah keras tu, someone in my mum group mentioned that soaking with a powder fabric cleaner like Loxus in hot water works really well, just pour the powder, add hot water, and let it soak for a while before washing as usual. Some mums love how simple it is, though a few did say you need to be careful with coloured fabrics just in case. Kalau stain tu jenis dakwat atau food stain yang degil, a good soak for at least 30 minutes usually does the trick before you give it a proper wash. Hope this helps, and good luck!