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You can check my BLOG here

DECLARE @data VARCHAR(100)
SET @data = '!2131231Atif123123 234234Sheikh6546'
WHILE PATINDEX('%[^a-z ]%', @data) > 0 
      SET @data = STUFF(@data, PATINDEX('%[^a-z ]%', @data), 1, '') 
SELECT
    RTRIM(LTRIM(@data)) AS Data