Scholars have differed as to specifying whether it is the `Asr (Afternoon), Fajr (Dawn), Zhuhr (Noon), Maghrib (Sunset), or `Isha' (Night) Prayer, or whether it is one of the five obligatory Salah (prayers) but which one is unclear. It is most likely to be the `Asr Prayer, based on what is related in the Two Sahih (authentic) Books (i.e. Al-Bukhari and Muslim) that the Prophet (peace be upon him) said,
They kept us so busy that we could not offer Al-Salat-ul-Wusta until the sun had set.
In another narration related by
Muslim, he (peace be upon him) said,
They kept us so busy that we could not offer Al-Salat-ul-Wusta, the `Asr Prayer.
And Allah knows best.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.