Fast doesn’t become invalid in these situations
If one eats or drinks or gets physical and intimate with one’s spouse unintentionally or due to forgetfulness or accidentally.
Even if an insect, smoke, or grain dust (due to handling in any manner) of wheat, barley, oat, etc. enters the throat.
If one applies hair oil or wears Surma (Kohl/antimony) and even if the taste is felt/realised. And even if the surma’s color appears in the saliva, the fast will not be rendered invalid.
If one experiences involuntary ejaculation (nightfall), the fast will still remain valid and intact.
If after establishing a physical relationship with the spouse one doesn’t perform Ghusl (Obligatory bath), and starts to fast and completes it at Maghrib, the fast will be considered valid. However, failing to perform Salaah will be an enormously grave sin.
If one uses a syringe to inject medicine, in the flesh or into the vein, the fast will not be considered invalid.
The fast is not rendered invalid even if one is inflected with any kind of wound . And as a result even if blood starts flowing/draining out of the body. Voluntary extraction of blood is prohibited while one is still fasting, because it might cause weakness. Any act that causes weakness is considered Makrooh (disliked/abominable/detested) while one’s fasting.
Also, if blood is injected into the vein the fast will still remain intact and valid.
Brushing one’s teeth is a makrooh act (act that is frowned upon). Moreover, if while brushing the foam/paste happens to start going down the throat, the fast will be rendered invalid.
If ejaculation doesn’t occur upon pecking and/or kissing one’s spouse, the fast is still intact.
The fast will not be rendered invalid even if – one looks at women’s private parts (but doesn’t touch them) and has the semen flowing out; or if thoughts of physical intimacy occur repeatedly and semen starts flowing out.
If anything the size of sesame, or a sesame seed itself, is chewed and swallowed the fast still remains intact and valid. However, if its taste is felt/realised while or after swallowing, THEN the fast is rendered invalid.
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