Double-check the data and make sure they are all correctly entered as dates and now some weird text. Both the TEXT and WEEKDAY formula should have produced correct results. There must be something else going on that we're not aware of.
I am surprised, but when i use =WEEKDAY(A1)=1 and click on APPLY button. It was showing wrong sunday. After that i have double check and it was surprising. Formula was changed it self (=WEEKDAY(A1048574)=1) after that i have correct formula again and apply.. The result is that what exact i want.
Thanks a lot Key Master, Thanks a lot Luke M for giving me Double check Idea..