Is it obligatory to say the Adhan or just the Iqamah for one who missed congregational prayer while he is in the mosque?

The scholars have agreed on the permissibility of a person praying alone without the adhan or iqama, suffice it for him to rely on the adhan and iqama of the mosque. It is preferable for him to perform the iqama, and it is most complete for him to perform both the adhan and the iqama, because the adhan and iqama are remembrances of Allah the Almighty. This is supported by what is authentically reported from Anas ibn Malik (may Allah be pleased with him), and what Sa'id ibn al-Musayyib and Imam al-Shafi'i held. If he performs the adhan, it is preferable for him not to raise his voice with it so as not to cause confusion among the people.