Hazrat Zaid bin Salat reports that Hazrat Umar, if he saw a trace of semen on his clothes, would wash it off, and if he did not see any trace, he would sprinkle water over it and repeat the prayer at the time of Duha.

Hazrat Sulayman bin Yasar narrates that Hazrat Umar offered the Fajr prayer, then went towards his land at the place of Juruf. There he saw a sign of nocturnal emission on his clothes, so he performed ghusl and repeated the Fajr prayer.

Hazrat Aflah says that I had performed the prayer while there was a stain of impurity on my clothes. Hazrat Ibn Umar (may Allah be pleased with them both) ordered me to repeat the prayer.

Ibrahim, regarding the person who prays while there is a stain of impurity on his clothes, says that his prayer is valid and he does not need to repeat it.

Hasan used to say that if one becomes aware during the time of prayer, he should repeat it.

Hazrat Saeed bin Musayyib says that whoever performed prayer with the sign of impurity (janabah) upon him, it is not obligatory for him to repeat it.

Ibrahim says that if a person sees traces of blood or semen on his clothes, he should wash them and not repeat the prayer.