The Prophet (peace be upon him) used to start Salat-ul-Layl (optional Prayer at night) with two short Rak`ahs, and then go on praying long Rak`ahs. It is authentically reported on the authority of
`Aishah (may Allah be pleased with her) that she said:
The Prophet (peace be upon him) used to offer four Rak`ahs - let alone their beauty and length - and then he would offer other four Rak`ahs - let alone their beauty and length - and then he would offer three Rak`ahs.
According to another narration by Al-Bukhari and Muslim, she (may Allah be pleased with her) said:
He (peace be upon him) used to offer ten Rak`ahs (at night), offering Taslim after each two Rak`ahs and then offer a single Rak`ah as Witr.
The wording of this Hadith interprets the one before it. It can be concluded from it that each two Rak`ahs are ended with Tashahhud and Taslim (salutation of peace ending the Prayer). This is what the prophet (peace be upon him) usually did. There are other forms authentically attributed to the Prophet (peace be upon him) in Tahajjud (optional late night Prayer), which are mentioned by
Muslim in his Sahih and other scholars as well. You can refer to them if you wish.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family and Companions.