You may fast without suhur for any fast obligatory (like in Ramadan or in case you need to make up missed fasts of Ramadan or a fast in fulfilment of a vow) or optional (like for the day of 'Arafa or 6 days of shwwal etc.).

Suhur is an optional thing and not mandatory else there would be evidences that fasting without suhur is void, which is not the case.

However it is highly recommended to do it (as it helps to strengthen one self):

Shaykh Ibn Baaz (may Allaah have mercy on him) said: “Suhoor is not a condition for fasting to be valid, rather it is mustahabb (recommended), (Source islamqa #20135)

Some evidences from the sunnah:

• "Take Suhur as there is a blessing in it." (See for example in Sahih al-Bukhari, Sahih Muslim)

• The difference between our fasting and that of the people of the Book is eating shortly before dawn. (See fore example in Sahih Muslim)

and also in the Qur'an one is asked to eat (during the night) before starting the day of fast:

... And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. ... (2:187)

Well one may say this applies for Ramadan, as this is the context of the verse, but eating in the night already is considered as suhur and is not necessary to have suhur until right before the adhan of the fajr prayer.

Finally this hadith:

The Apostle of Allah (ﷺ) came to me one day and said: Is there anything with you (to eat)? I said: No. Thereupon he said: I shall then be fasting. Then he came to us another day and we said: Messenger of Allah, hais has been offered to us as a gift. Thereupon he said: Show that to me; I had been fasting since morning. He then ate it. (Sahih Mulsim)

is often used as an evidence that performing the niyyah (before fajr) for optional fasts is not necessary (which is rejected in the maliki school of fiqh) and shows that the Prophet () didn't have a suhur and decided to fast that day!

You may fast without suhur for any fast obligatory (like in Ramadan or in case you need to make up missed fasts of Ramadan or a fast in fulfilment of a vow) or optional (like for the day of 'Arafa or 6 days of Shawwal etc.).

Suhur is an optional thing and not mandatory else there would be evidences that fasting without suhur is void, which is not the case.

However it is highly recommended to do it (as it helps to strengthen one self):

Shaykh Ibn Baaz (may Allaah have mercy on him) said: “Suhoor is not a condition for fasting to be valid, rather it is mustahabb (recommended), (Source islamqa #20135)

Some evidences from the sunnah:

• "Take Suhur as there is a blessing in it." (See for example in Sahih al-Bukhari, Sahih Muslim)

• The difference between our fasting and that of the people of the Book is eating shortly before dawn. (See fore example in Sahih Muslim)

and also in the Qur'an one is asked to eat (during the night) before starting the day of fast:

... And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. ... (2:187)

Well one may say this applies for Ramadan, as this is the context of the verse, but eating in the night already is considered as suhur and is not necessary to have suhur until right before the adhan of the fajr prayer.

Finally this hadith:

The Apostle of Allah (ﷺ) came to me one day and said: Is there anything with you (to eat)? I said: No. Thereupon he said: I shall then be fasting. Then he came to us another day and we said: Messenger of Allah, hais has been offered to us as a gift. Thereupon he said: Show that to me; I had been fasting since morning. He then ate it. (Sahih Mulsim)

is often used as an evidence that performing the niyyah (before fajr) for optional fasts is not necessary (which is rejected in the maliki school of fiqh) and shows that the Prophet () didn't have a suhur and decided to fast that day!