Muqatil bin Sulaiman said: “Salât (prayer) was established as an obligatory ritual at an early stage of the Islamic Call, a two rak‘ ah (unit of prayer) Salât in the morning and the same in the evening;
“And glorify the praises of your Lord in the ‘Ashi (i.e. the time period after the mid-noon till sunset) and in the Ibkar (i.e. the time period from early morning or sunrise till before mid-noon).” [40:55]
Ibn Hijr said: “Definitely the Prophet (Peace be upon him) used to pray before ‘The Night Journey’ but it still remains a matter of controversy whether or not the prayer was established as an obligatory ritual before imposing the rules of the usual five prayers a day. It is related that obligatory prayer was established twice a day, in the morning before sunrise and after sunset. It is reported through a chain of narrators that when the Prophet (Peace be upon him) received the first Revelation, Gabriel - the angel, proceeded and taught him how to observe Wudu (ablution). When the Prophet (Peace be upon him) had finished, he took a handful of water and sprinkled it on his loins.
Ibn Hisham reported that when it was time for prayers, the Messenger of Allâh (Peace be upon him) and his Companions went into a mountain valley to pray secretly. Abu Talib once saw the Messenger of Allâh (Peace be upon him) and Ali praying, he asked them what they were up to. When he got to know that it was obligatory prayer, he told them to stay constant in their practice.