Were Muslims obligated to perform prayer during the first three years of the secret call to Islam, before the five daily prayers were ordained?

A group of scholars held that no obligatory prayers existed before the Isra' (Night Journey) except for the night prayer, which was not precisely defined. Al-Harbi, however, maintained that prayer was obligatory, consisting of two rak'ahs in the morning and two rak'ahs in the evening. Ash-Shafi'i mentioned that the night prayer was obligatory, then abrogated by Allah's saying: "So recite what is easy [for you] thereof." Then, the obligation of praying part of the night was abrogated by the five daily prayers. It is authentically narrated from 'Aishah (may Allah be pleased with her) that the night vigil (qiyam al-layl) was made obligatory at the beginning of Surat Al-Muzzammil, and the Prophet (peace be upon him) and his companions observed it for a full year. Then, the obligation was eased at the end of the surah, making the night vigil a voluntary act after having been an obligation. The difference of opinion regarding the abrogating text does not matter as long as there is agreement that the obligation of the night vigil has been abrogated.