There is no sahw (forgetfulness, i.e. doubts in regards to how many units one has performed) in the voluntary prayer, so whoever has sahw in a voluntary prayer then he is to build upon whatever he wants (i.e. in terms of which unit it is). Sahw is only in the obligatory prayer. So, someone who has sahw in the first two [units] is to repeat the prayer. Someone who doubts in the Maghrib is to repeat the prayer. Someone who doubts in the ghada is to repeat the prayer. Someone who doubts in the second and the third, or in the third and the fourth, then he is to build upon the most [i.e. the higher number]. So, when he has done taslim, he completes what he suspects he had decreased. The two sajda of sahw are not obligatory upon the praying person except for when he stood when he was in the state of sitting, or he sat in the state of standing, or he left off the tashahhud, or he did not know whether he added in his prayer or decreased from it. They are after the taslim in [a situation of] addition and decrease. In them it is said: bismillahi wa billaahi as-salamu `alayka ayyuha ‘n-nabiyyu wa rahmatullahi wa barakatuh (by the name of Allah and by Allah, peace be upon you O prophet and the mercy of Allah and His blessings).