Yes, there are few sunnahs that Muslims avoid thinking that it will break their fast or it is makroo. And the most important sunnah which people avoid during Ramadan is using Siwaak, using the tooth stick. Many Muslims feel that if they use it, it is makroo.

Main reason is there is a hadith of Muhammad (peace be upon him) mentioned in Sahih Bukhari which says, “I swear by Allah in whose hand is the soul of Muhammad that the breath of the person who fasts is more sweater to Allah than the scent of Musk”. Based on this hadith many Muslims think that the bad breath or the foul breath of the person who is fasting will not be there and it will not please Allah.

That’s the reason they avoid using the siwaak. These people fail to realize that when we use the stick, siwaak, it does not remove the foul breath or the breath which normally people don’t like of the person who fasts. The siwaak basically cleans the teeth, cleans the gum, it helps in keeping the teeth healthy but in no way it reduces the bad breath especially of a person who fasts.

And furthermore there is hadith of Prophet where Muhammad (peace be upon him) who said, “if it wouldn’t have been too hard for my Ummah I would have made it compulsory for them to use miswaak before every prayer”. And here he did not made any exceptions like he would have said, ‘I would have made compulsory for my ummah except during fasting…’ this important sunnah if it nullified or makroo the fast surely our beloved prophet (peace be upon him) would have mentioned it.

So this proves that it is a very important sunnah which Muslims should continue doing even during the month of Ramadan. It will not nullify their fast, it is not makroo, and instead it is ‘mustahab’, its encouraged.

Another important sunnah which people neglect or avoid fearing that it will spoil their fast or nullify their fast is putting water in nostrils, sniffing water in the nostrils especially during wudhu. So many of the Muslims even when they do wudhu they just get the water close to their nose and touch the tip of the nose with it and that’s it.

They do not put the water in their nostrils and clean them which is a requirement for wudhu. Water entering your nose into your throat will nullify your fast! But the chances are way negligible. What our beloved Muhammad (paece be upon him) said, “when you do wudhu sniff the water excessively except in fasting”. So normally when we do wudhu we sniff the water excessively except in fasting.

Because in fasting if we sniff excessively there are chances, though very negligible that water may enter our throat and nullify our fast. But normally it does not happen. It is a very important sunnah which many Muslims avoid.

(Source - Dr Zakir Naik Lecture)