What is the correct number of rak'ahs for Qiyam al-Layl in a single tasleem: is it four rak'ahs followed by a tasleem, or is it prayed two rak'ahs by two rak'ahs?

The night prayer is two by two. The Prophet (peace be upon him) did not exceed eleven rak'ahs, neither in Ramadan nor at other times. He would pray four rak'ahs—do not ask about their excellence and length—then pray four rak'ahs—do not ask about their excellence and length—then pray three rak'ahs.

Sheikh Ibn Uthaymin clarified that the hadith of Aishah (may Allah be pleased with her) suggests that the first four rak'ahs could have been with one taslim, the second four with one taslim, and the remaining three with one taslim.

The more probable interpretation is that he used to pray two rak'ahs by two rak'ahs, but after the first four, he would sit to rest and regain his energy. Similarly, after the second four, he would pray two rak'ahs by two rak'ahs and then sit to rest and regain his energy.

This is supported by his (peace and blessings be upon him) saying: "The night prayer is two by two." This reconciles his actions and his saying (peace and blessings be upon him).