Abu Hurairah (RA) reported Allah's Apostle (ﷺ) as saying When any 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