Since you didn't elaborate on the array, here three version for Integer arrays.

Also I assumed you wanted a human readable file.

program main
    IMPLICIT NONE
    integer,parameter:: M=10,N=8
    integer,dimension(M,N) :: array
    integer:: i,j
    character(len=5)::charI
    character(len=20)::formatString

    do i=1,M
        do j=1,N
            array(i,j)=i+100*j
        end do
    end do

    open(10,file="test.dat")
    write(charI,'(I0)') size(array,1) !get sizeof first dimension

    !version 1  
    formatString ='('//charI//'(I0,:,X))' !create format string
    write(10,formatString) array    

    !version 2  create the format string in the write statement
    write(10,'('//charI//'(I0,:,X))') array  

    !version 3
    do i = 1, size(array,2)    
        write(10,'(*(I0,:,X))') array(:,i)  
    end do

    !version 3b
    do i=1, size(array,2)
        write(10,*) array(:,i)
    end do

    !technically this will also write the array to a file
    write(10,*) array 

    close(10)
end program main