Narrated Abu Hurairah: The Messenger of Allah ﷺ as saying: When one of you gets up at night, he should begin the prayer with two short rak'ahs.
Related hadith on this topic
Explanation & Benefits
Shaykh Muhammad Ibrahim bin Basheer
Benefit:
The first two units (rak‘ahs) of the Tahajjud prayer should be performed lightly; this applies to certain occasions, and at other times the Prophet sallallahu alayhi wa sallam would perform the first two units of Tahajjud for a longer duration. [صحيح مسلم : 763، 1792]
Source: Musnad al-Humaydi: Commentary by Muhammad Ibrahim bin Bashir, Page: 1014