rbuh was in a state of sexual impurity at the break of dawn he pbuh would perform ghusl after the fajr adhan and observe the fast. and he rbuh might kiss one of his wives while fasting in ramadhan and compared it to rinsing the mouth with water.
his guidance concerning eating or drinking out of forgetfulness
he pbuh ruled that a fasting person need not make up the day if he ate or drank out of forgetfulness, saying that it was allah the almighty who had fed him and given him drink. so one is not held responsible for that food and drink and it does not break his fast since it is only broken by what he does deliberately. it is like eating or drinking in one's sleep, and the acts of someone asleep or someone who has forgotten are not accountable.
what breaks or invalidates the fast
the prophet pbuh stated that the fast is broken by deliberate eating or drinking, drawing blood (cupping) and vomiting.
the qur'an states that sexual intercourse invalidates the fast, as does eating and drinking, and there is no disagreement over this.
he pbuh did not mention anything about applying kohl, but it is reported that he pbuh would use the tooth stick (miswak) while fasting. and he pbuh did not forbid using the miswak no matter whether early or late in the day. imam ahmad mentioned that he would pour water on his head while fasting. and he used to take water into his mouth and nose while fasting but warned people not to take it too deeply into the mouth. imam ahmad also said that he pbuh would not have himself cupped while fasting.
his guidance in i`tikaaf 
he pbuh performed i`tikaaf regularly during the last ten days of ramadhan until his death. once he missed it in ramadhan but made up the days during the month of shawwal.
he pbuh once did i`tikaaf in the first ten days of ramadhan, then in the middle ten days, then in the last ten days, seeking laylatul-qadr. after that it became clear to him that it comes within the last ten days, so he continued to do it then until he died.
he used to order that a tent be set up for him in the mosque in which to seclude himself with his lord. when intending i`tikaaf, he would begin it after performing the fajr prayer.
he used to perform i`tikaaf ten days every year, and in the year before he pbuh died he did it for twenty days. angel jibreel would come to hear his recitation of the qur'an once every year, but in his final year he came to hear it twice. and jibreel would recite it to him every year but recited it to him twice that year.
when he pbuh performed i`tikaaf he would enter his tent alone. he would only go to his house for answering a call of nature. from the masjid he used to put his head into aisha’s room for her to comb and wash his hair, even when she had her menses.
one of his wives would visit him during his i`tikaaf, and when she would get up to leave he would stand up and accompany her to the door, and that was at night. he did not have sexual relations with any of his wives during i`tikaaf, neither kissing nor anything else.
during i`tikaaf he would have his mattress and bed put in the place where he stayed. when he went out to relieve himself he might pass a sick person on the way and not stop or ask about him.
once he pbuh performed i`tikaaf in a turkish tent and placed a straw mat over its entry in order to achieve the objective and spirit of i`tikaaf (seclusion). this is in contrast to the practice of ignorant people who make it a place for gathering friends and visitors to converse among themselves. theirs is one way, but the i`tikaaf of the prophet was another. and allah the almighty is the giver of success.