WITH input_dates ( start_date, end_date ) AS ( 
  SELECT DATE '2018-01-03', DATE '2018-01-31' 
  FROM   DUAL 
), 
valid_start_date ( start_date, end_date ) AS ( 
  SELECT CASE 
         WHEN start_date - TRUNC( start_date, 'IW' ) 
                IN ( 
                  0, -- Monday 
                  1, -- Tuesday 
                  2, -- Wednesday 
                  3, -- Thursday 
                  6  -- Sunday 
                ) 
         THEN start_date 
         ELSE NEXT_DAY( start_date, 'SUNDAY' ) 
         END, 
         end_date 
  FROM   input_dates 
), 
dates ( start_week, end_week, end_date ) AS ( 
  SELECT start_date, 
         LEAST( NEXT_DAY( start_date, 'THURSDAY' ), end_date ), 
         end_date 
  FROM   valid_start_date 
  WHERE  start_date <= end_date 
UNION ALL 
  SELECT NEXT_DAY( start_week, 'SUNDAY' ), 
         LEAST( end_week + INTERVAL '7' DAY, end_date ), 
         end_date 
  FROM   dates 
  WHERE  NEXT_DAY( start_week, 'SUNDAY' ) <= end_date 
) 
SELECT start_week, end_week 
FROM   dates

WITH input_dates ( start_date, end_date ) AS (   
  SELECT DATE '2018-01-03', DATE '2018-01-31'   
  FROM   DUAL   
),   
valid_start_date ( start_date, end_date ) AS (   
  SELECT CASE   
         WHEN start_date - TRUNC( start_date, 'IW' )   
                IN (   
                  0, -- Monday   
                  1, -- Tuesday   
                  2, -- Wednesday   
                  3, -- Thursday   
                  6  -- Sunday   
                )   
         THEN start_date   
         ELSE NEXT_DAY( start_date, 'SUNDAY' )   
         END,   
         end_date   
  FROM   input_dates   
)  
SELECT CASE 
       WHEN LEVEL = 1 
       THEN START_DATE 
       ELSE NEXT_DAY ( START_DATE - INTERVAL '7' DAY, 'SUNDAY' ) + (LEVEL - 1) * 7 
       END AS start_week, 
       LEAST( 
         NEXT_DAY ( START_DATE - INTERVAL '1' DAY, 'THURSDAY' ) + (LEVEL - 1) * 7, 
         end_date 
       ) AS end_week 
FROM   valid_start_date  
CONNECT BY 
       CASE 
       WHEN LEVEL = 1 
       THEN START_DATE 
       ELSE NEXT_DAY ( START_DATE - INTERVAL '7' DAY, 'SUNDAY' ) + (LEVEL - 1) * 7 
       END <= end_date