Eating apples strengthens the heart (Al-Suyuti).
Forgetfulness can be brought on by, amongst other things, eating sour apples (the others include cupping on the nape of the neck and excessive eating of coriander) (Al-Jawziyya).
Impatient hunger can be dealt with by apple juice and pomegranate juice (Chishti).
Apple Cider Vinegar
The Prophet (peace be upon him) was reported to have once remarked that vinegar was the seasoning of all the prophets who came before him. Prophet Muhammad (peace be upon him) liked vinegar. Jabir narrated, "The Messenger of Allah, peace be upon him, took me one day with him to his house. He was served some bread. He asked: 'Is there any dip?' They replied 'No, only some vinegar.' He said, 'Vinegar is a good dip.' Jabir used to say, "I have loved vinegar since I heard it from Allah’s Prophet". Naf'a said, "I have loved vinegar since I heard it from Jabir." [Muslim, Abu Dawud, Nasa’i].
Apple cider vinegar is produced from unprocessed apple juice and vinegar. It keeps the apple's colour and flavour. There is now a wealth of evidence as to the wide range of benefits of consuming apple cider vinegar regularly.
Chishti advises that oxymel is 1 part vinegar 5 parts honey.
Unani medicine says oxymel was a great tonic for purifying the body of excessive, morbid or aggravated black bile or intermittent fevers.
Oxymel is the base on which one builds all kinds of herbal treatments. For example, pomegranate oxymel to strengthen the stomach. As a side note, an informative Tibb website gives some valuable information about making vinegar and declares pomegranate vinegar the king of vinegars.
Basic oxymel is simple and easy to prepare. The sharp aroma of the vinegar leads one to think the taste is going to be little unpleasant, but it is not.
Al-Suyuti "Medicine of the Prophet" - Islamic Society
Ibn Qayyim Al-Jawziyya "Medicine of the Prophet" - Islamic Texts Society
Chishti "The Traditional Healers Handbook" Simon & Schuster