Try:

=SUMPRODUCT(--(TEXT(Sheet1!$A$2:$A$100,"mmmm")=B2),--(Sheet1!$B$2:$B$100=A2),--(Sheet1!$C$2:$C$100=C2),(Sheet1!$D$2:$D$100))

Sheet1 is your data sheet.

Place formula in your report sheet column D and copy down. I have assumed
Columns A to C in report sheet have Salesman, Month (in words) and Product
data in place.

Change ranges to suit: note with SUMPRODUCT you cannot use whole columns
i.e. A:A is not allowed.

HTH

"Kelvin Lee" wrote:

In my column A is a date record (dd/mm/yy), column B is salesman, column C is
product sold and Column D is the quantity value of product sold.

I wish to have a report which in column A is the salesman, B is the month
(January - December in words), C is the product and D is the sum of the
particular month and particular goods had sold.

Without having an extra column to record in the month in words. How can I
capture the value by month with using SUMIF since the format is dd/mm/yy?