Musannaf Ibn Abi Shaybah

Hazrat Ata and Hazrat Tawus state that if a person performs eight circuits in Tawaf and remembers before offering the two rak'ahs, then he should perform another Tawaf with six circuits and then offer four rak'ahs. And if he remembers after offering the two rak'ahs, then he should perform six more circuits of Tawaf and offer two more rak'ahs, and if he wishes, he may choose not to count them.

Hasan says that if eight circuits of Tawaf are performed, (still) two rak‘ahs will be offered.