Are the rulings pertaining to obligatory fasting applicable to voluntary fasting insofar as the two following points are concerned: 1- if the person observing a voluntary fast forgetfully eats or drinks, should he continue fasting, and 2- will the supplication made before iftar (the time for fast-breaking) during voluntary fasting be answered just like the supplication made in Ramadan?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

There is no difference between voluntary and obligatory fasting concerning the ruling on forgetfully eating or drinking. However, in case of obligatory fasting, the fasting person must continue fasting and is not required to make up for the fast later. In case of voluntary fasting, the fasting person is merely recommended to continue fasting. This is because the person performing a voluntary fast is free either to continue or break his fasting whether or not he forgetfully eats or drinks during the fast. ‘Aa’ishah said to the Prophet, sallallaahu ‘alayhi wa sallam, "O Messenger of Allaah! We have been gifted with hays (a type of food)." The Prophet, sallallaahu ‘alayhi wa sallam, said to ‘Aa’ishah, "Fetch it for me as I have been fasting since the morning," and he ate from it." [Muslim] According to another narration, the Prophet, sallallaahu ‘alayhi wa sallam, added: "The one who has decided to observe a voluntary fast is like the one who has decided to give a voluntary charity.  He may give it if he so wishes and withhold it if he so wishes." [An-Nasaa’i]

The Prophet, sallallaahu ‘alayhi wa sallam, also said: "The one observing a voluntary fast is free to continue or to break his fast (he is not obliged to complete it). He may complete his fast or break it as wishes.” [Ahmad and At-Tirmithi] In Kashf Al-Khafaa’, Al-‘Ajlooni says, “This hadith has an authentic chain of transmission. However, it is recommended that the Muslim makes up for the voluntary fast that he voluntarily breaks.”

Answering the supplication of the fasting person at iftar time is a privilege for whoever is fasting, whether the fast is obligatory or voluntary. This is because there is no textual evidence that differentiates between obligatory and voluntary fasting in this regard.

Allaah Knows best.