Sahih Al Bukhari Hadith Number 754

Narrated Anas: While the Muslims were offering the Fajr prayer, Allah’s Messenger (peace be upon him) suddenly appeared before them by living the curtain of the dwelling place of `Aisha, looked towards the Muslims who were standing in rows. He smiled with pleasure. Abu Bakr started retreating to join the row on the assumption that the Prophet wanted to come out for the prayer. The Muslims intended to leave the prayer (and were on the verge of being put to trial), but the Prophet (peace be upon him) beckoned them to complete their prayer and then he let the curtain fall. He died in the last hours of that day.

10  Call to Prayers (Adhaan)
Hadith number 754
Volume no 1
Chapter: 94 (Is it permissible to one to look around in Salat (prayer) if something happens to one? Or can one look at something like expectoration in the directn of the Qiblah?)