Contrary to the statement of the person who says that they can be performed while the Imam is performing the obligatory prayer.

Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates from the Noble Prophet (peace and blessings be upon him) that he (peace be upon him) said: "When the (congregational) prayer is established, then there is no prayer except the obligatory prayer."

Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the iqamah for the (obligatory) prayer was given and I had not yet performed the two sunnah (units), so the Prophet (peace and blessings be upon him) saw me performing the two sunnah and he forbade me and pulled me and said: "Do you want to pray four rak‘ahs of Fajr?" Abu ‘Amir Salih bin Rustam was asked, "Did the Prophet (peace and blessings be upon him) say this?" He replied, "Yes." Ibn Abi Mulaykah narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that he said: The iqamah for the (Fajr) prayer was given, so I stood up and began to perform the two sunnah units—then the Messenger of Allah (peace and blessings be upon him) caught me and pulled me and said: "Will you pray four rak‘ahs of Fajr?"

Sayyiduna Abdullah bin Sarjis (may Allah be pleased with him) narrates that a man came while the Messenger of Allah (peace and blessings be upon him) was leading the morning prayer. So he performed two Sunnah (units of prayer) first (then joined the congregation). Then when the Messenger of Allah (peace and blessings be upon him) completed his prayer, he said: "O so-and-so, which prayer did you count as obligatory—the one you prayed with us or the one you prayed alone?" These are the words of the hadith of Hammad bin Zaid.

Sayyiduna Anas (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) came out while the iqamah had already been pronounced, and he saw some people hastily performing two rak‘ahs (of Sunnah). The Prophet (peace and blessings be upon him) said: "Do you want to combine two prayers together?" Therefore, the Prophet (peace and blessings be upon him) forbade performing prayer in the mosque after the iqamah had been pronounced.

Sharik narrated from Sayyiduna Anas (may Allah be pleased with him) a hadith similar to the above-mentioned narration up to the words: "Do you want to combine two prayers together?"

Muhammad bin Ishaq states that this narration has been reported by Imam Malik bin Anas and Isma‘il bin Ja‘far from Sharik bin Abi Numayr, from Abu Salamah, as a mursal narration. And Ibrahim bin Tahman narrated both these ahadith from Sharik, from Sayyiduna Anas and Abu Salamah (may Allah be pleased with them). Ibrahim bin Tahman narrated both ahadith with separate chains: the hadith of Sayyiduna Anas (may Allah be pleased with him) separately, and the narration of Sayyiduna Abu Salamah (may Allah be pleased with him) with a separate chain.