Answer:
After doing istibraa’, one should properly clean one’s private parts. For this, it is best to use both toilet paper and water (firstly he should wipe with toilet paper then he should wash with water). Second best is to use only water. Third best is to only use toilet paper.
However, if the urine has spread to an area more than the size of a dirham (2.75 cm in diameter), then it is compulsory to use water. One cannot suffice only on toilet paper in this case. Similarly, in the case of expelling stool, if the stool has spread around the private part and is more than the weight of a dirham (4.86 grams — regardless of size) then using water is compulsory; one cannot suffice on toilet paper in this case too.
When using toilet paper, it is mustahabb (preferable) to use an odd number (3 upwards). Therefore, even if one attained cleanliness using one or two pieces of toilet paper, it will be preferable for him to use three pieces.
If one needs to clean both his back private part as well as the front one, he should begin with the back one. This will help to expel the last drops of urine from the front private part.
When washing the back private part with water, he should wash properly until he is satisfied that the area is clean. If he is not fasting, he should relax the back private part, as this will help to clean the impurity that did not fully expel. He should wash his private part until the bad smell on the private part and on his fingers is removed (unless it is hard to do so), as this will ensure cleanliness.
After washing the private parts, one should dry them (by wiping with toilet paper, for example). (Maraaqil Falaah; Tahtawi; Imdaadul Fattaah)
Mufti Faizal Riza