What were the stages of fasting before it was abrogated to its current form?

The first fast mandated by the Prophet, peace and blessings be upon him, was the fast of Ashura. Then, the fasting of Ramadan was made obligatory in the second year of the Hijra. The obligation of fasting Ramadan went through three stages:

1. The first stage: Choosing between fasting or breaking the fast with feeding a poor person. The verse: ﴿And upon those who are able to fast, but with difficulty - a ransom [as substitute] is feeding a poor person. But whoever volunteers excess - it is better for him. And that you fast is better for you, if you only knew.﴾ (Al-Baqarah/184) was evidence for this, then it was abrogated by the verse that followed it.

2. The second stage: Obligating the capable person to fast, removing the option. The evidence for this is the Almighty's saying: ﴿The month of Ramadan in which was revealed the Qur’an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it.﴾ (Al-Baqarah/185).

3. The third stage: Permitting eating, drinking, and marital intimacy during the night after sleeping. In the beginning of the obligation, if one slept before eating and drinking, it was forbidden for him until the next night. Then this ruling was abrogated by the Almighty's saying: ﴿It has been made lawful for you the night of fasting to approach your wives,﴾ and His saying: ﴿And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night].﴾

After that, other voluntary fasts were legislated gradually.