Jazaka Allah for your help.
Your Dream is short, to the point, and contains both glad tidings and a warning to you. Here is why I say this :
#1 For Rasul Allah s.a.w to appear to your sister in your dream and him (s.a.w) indirectly informing your sister to inform you to take ablution is a good sign. I believe it’s a blessing. A message from Rasul Allah s.a.w is very auspicious and full of meaning for the person it is meant and a glad tidings
#2 Having said that, the bone of contention is your behavior in real life. Although you might be an honest and religious person but at the same time you are stubborn and do not change your views easily. Further you may not consider other people advise seriously for which you may have suffered morally , spiritually and financially in the past but you are not the one who would admit his mistakes. The reason why Rasul Allah s.a.w appeared to your sister and not to you is ” you are not keeping yourself clean physically”
You must take immediate action now that the message has been delivered to you indirectly. Be careful especially after urination. Don’t let any of it get unto your clothes that you wear for Salah (namaz).Take ablution often. Also try to relax and open up to other people’s suggestions and advise in real life.
Inshallah if you follow on this advise of Rasul Allah s.a.w, may Allah bless you with the appearance ,in the dream ,of Rasul Allah SalalAllaho Walaiwasalam like HE has blessed me with his (s.a.w.) appearance in my dreams. Aameen.
If this interpretation has helped you brother pray for my magfarat and jannah.