That which does not nullify the fast

1) to mistakenly or forgetfully eat and drink; thereby one is not required to make up the fast nor pay a penalty.

the messenger of allah (peace be upon him) said:

((whoever forgets whilst fasting and then eats or drinks then he should complete his fast for verily it is allah who provided him the food and water)),

[the authenticity of this narration has been agreed upon by al-bukhaaree and muslim]

the messenger of allah (peace be upon him) also said:

((indeed allah has overlooked that which the ummah falls into as a mistake or out of forgetfulness or that which they are forced to do)),

[saheeh, transmitted by at-tabaraanee] 

2) unintentional vomitting.

the messenger of allah (peace be upon him) said:

((whoever is overcome by vomitting whilst fasting, then he is not required to make up the fast)),

[saheeh, transmitted by al-haakim]

3) using the miswaak (tooth stick) at all times, and likewise using a toothbrush and toothpaste. 

4) gargling water and sniffing water up the nose and blowing it out, so long as none of this is done excessively.

the messenger of allah (peace be upon him) said to al-qayt ibn saburah from the tribe of banee al-muntafiq:

((perform the wudhoo. and wash between the fingers and exaggerate in sniffing water up the nose and blowing it out, unless you are fasting)),

[saheeh, transmitted by abu daawood, at-tirmidhee, ibn maajah and an-nasaa.ee] 

5) applying kohl to the eyes and applying medical solution drops to the ears and the eyes, even if you find the taste reaches your throat; 

6) to taste food, with the condition nothing passes the throat to the stomach;

7) a young or old man kissing his wife so long as it does not lead to sexual intercourse, as the prophet (peace be upon him) used to kiss 'aa.ishah whilst he was fasting,

[the authenticity of this narration has been agreed upon by al-bukhaaree and muslim] 

8) taking a necessary injection so long as it is not nutrition-based, i.e. a substitute for food, etc; 

9) to swallow saliva or phlegm and that which one is unable to avoid such as dust and the like;

10) the application of medication which does not enter the stomach such as creams/ointments and the (medical) pump for asthma sufferers;

11) having a tooth removed or blood coming out of the nose or mouth;

12) to chew gum which (does not dissolve and thereby pass the throat into the stomach) does not have any taste;

13) if the time for fajr has entered whilst the bowl of food is in your hands, then do not put it down until you have satisfied your need.

the messenger of allah (sal-allahu 'alayhe wa sallam) said:

((if any of you hear the call (to he fajr prayer) whilst the bowl (of food) is in your hands, then do not put it down until you have satisfied your need from it)),

[saheeh, transmitted by abu daawood] 

14) delaying taking the ghusl if one is in a state of janaabah or post-menses or post partum bleeding until after the time of fajr has entered. however, it is better to hasten to take the ghusl so as to offer the fajr prayer on time; 

15) to perfume oneself with oils or atomisers, and not incense-based perfumes;

16) taking a bath to cool oneself down or out of thirst and heat or other than this.