The daytime prayer: how many rakahs at a time?

It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The prayer of the night and of the day is two rak'ahs, two rak'ahs." In Ghundar's narration the words are: "two at a time (mathna mathna)."

Sayyiduna Ibn Umar (may Allah be pleased with them both) used to pray four rak'ahs at a time in the daytime.

Yahya said: Four rak'ahs at a time.

Ibrahim said: The day prayer is four rak'ahs at a time; this applies to voluntary prayer.

Ibn Awn said: I asked Nafi' about voluntary prayers in the daytime, how many rak'ahs they should be prayed in. He said: "As for me, I pray four."

Ibn Awn said: I mentioned this to Muhammad (Ibn Sirin), and he said: "Is not praying two rak'ahs [at a time] the more soundly preserved way?"

Al-Hasan said: The prayer of the night and the prayer of the day are two rak'ahs at a time.

Hanzalah bin Abd al-Karim said: I asked Hammad about the daytime prayer, and he said: "Two rak'ahs at a time."

Habib bin Abi Amrah said: Sa'id bin Jubayr used to pray voluntary prayers by night and by day, two rak'ahs at a time.