Prayers and Fasts in the State of Janābah
One should makes up for the prayers said in the state of janābah. Their fasts are valid if they did not know that they were in the state of janābah or they did not know what janābah is. However, if they knew they were in the state of janābah but did not know that making ghusl was obligatory, they should make up for the fasts yet kaffārah is not required.

Forgetting Ghusl of Janābah
During the month of Ramadan, if one forgets to perform the ghusl of janābah at night before morning adhān, his fast is void. As per caution, the same rule applies to the qaḍā’ of Ramadan fasts. However, it does not invalidate other fasts.

To Discharge Semen due to Foreplay
If a fasting person makes foreplay with someone or excites his own private parts — without intention to discharge semen while he was not used to discharge semen due to it — but semen gets out, his fast is valid although it leads to discharge of semen. However, if he continues to do so even after he is on the verge of discharging semen so that semen is discharged, his fast is invalid. 

To Menstruate during a Nadhr Fast
If a woman's menstrual cycle starts while she is fasting — as she made nadhr to fast that day, her fast is invalidated and she has to perform its qaḍā’ after she is clean again.

Gargling during Fast
It invalidates the fast if water goes down the throat while gargling.

To Swallow Sputum
There is no problem in swallowing sputum which has not reached the mouth cavity. If it reaches the mouth cavity, one should avoid swallowing it by obligatory caution. If one swallows it intentionaly, he should, by obligatory caution, make up for his fast and pay kaffārah as well.

Smoking
By obligatory caution, a fasting person should avoid all kinds of smoking and fasting does not cease to be obligatory even if smoking becomes necessary.

Injection/Infusion during Fast
It is based on obligatory caution for the fasting person to avoid having any kind of supportive, nutritional or intravenous injections. The same rule is applied to all kinds of intravenous fluid/blood infusions. However, there is no objection to using anesthetic injections and intramuscular ones for treatment purposes.  

Ghusl by Immersion during Fast
If one performs ghusl by immersion out of forgetfulness (of the fact that he is fasting) or negligence, then both his fast and ghusl are valid. 

To Break One's Fast Too Early 
It is not permissible for a mukallaf to follow others in breaking the fast unless there is shar‘ī evidence that it is maghrib time. If it is a case of dissimulation, they can break their fast but they should make it up in qaḍā’. 

Not Knowing a Fast Invalidator
If someone does not know that an act such as taking medicine invalidates fasting and does so, he should perform its qaḍā’ but paying kaffārah is not required.