It is not a necessary condition that the six days of Shawwal should be fasted consecutively. If you fast them separately or consecutively, it is OK.

Whoever fasts six days of Shawwal will have recorded for him a reward as if he had fasted a whole year. For more, please see the detailed answer.

1. The day of ‘Ashura is one of the significant days on which the Prophet (peace be upon him) prescribed we should fast. This day is not for Moosa (peace be upon him); rather it is for the saving of the believers. 2. The reason for fasting it is that it is the day on which Allah saved Moosa and drowned Pharaoh and his troops, and there covered them from the sea that which covered them. So the Prophet fasted on this day, and he enjoined the Sahaabah to fast on this day too. 3. When Allah enjoined fasting the month of Ramadan, this ruling was abrogated, and fasting on this day became Sunnah.

Some scholars view that so long as there is sufficient time to make up missed fasts, it is permissible to observe optional fasts.

If you intended to fast `Ashura but you didn’t fast deliberately, you will not get any reward. If you forgot to fast `Ashura, we hope you will get rewarded. If you didn’t fast `Ashura because of sickness, we hope you will get rewarded.

1-The Hadith which reads “Fasting on one of these days (the first ten days of Dhul-Hijjah) is equivalent to fasting for a year” has a da‘if isnad (weak chain of transmission) because of an-Nahhas ibn Qaham and and Mas‘ud ibn Wasil 2- The hadith which reads “There are five things that the Prophet (peace and blessings of Allah be upon him) never failed to do…” is based on the report narrated by Hunaydah ibn Khalid al-Khuza‘i, from whom it was narrated via many isnads, in several versions. The critics of hadith differed as to the classification of this hadith because each of these versions has its own isnad and text. For more, see the detailed answer.

In the case of a voluntary fast that is not done for a specific reason, it is not stipulated that the intention should be formed from the night before. But in the case of a voluntary fast that is done for a specific reason, it is essential to form the intention from the night before.