Is it necessary to wash the penis and anus for every ablution, even if there is no urine or feces, and is it sufficient to wash one of them without the other before ablution?

The traces of urine and feces must be removed from the private parts before performing ablution or prayer. It is preferable to wash with water after removing the substance itself with a stone, as the people of Quba' did. It is permissible to suffice with stones if the impurity has not spread. If the impurity is only urine, then the place of urination should be washed or wiped with three stones. If it is only feces, then its place should be washed or wiped. However, if the impurity is the emission of wind, then washing or wiping the front or back private parts is not prescribed.