There are many Sunnahs of fasting, including the following: 

1 – It is Sunnah if someone insults you to respond in a better manner and say, “I am fasting,” because of the report narrated by al-Bukhaari and Muslim from Abu Hurayrah (may Allaah be pleased with him), that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Fasting is a paradise so there should be no obscene or offensive talk or behaviour.

If a person fights him or insults him, let him say, ‘I am fasting,’ twice. By the One in Whose hand is my soul, the smell coming from the mouth of the fasting person is better before Allaah then the fragrance of musk. [Allaah says:] ‘He gives up his food, drink and desire for My sake. Fasting is for Me and I will reward for it, and a good deed receives the reward of ten like it.’” Al-Bukhaari, no. 1894; Muslim, 1151. 

2 – It is Sunnah for the fasting person to eat suhoor, because it was proven in al-Saheehayn that Anas ibn Maalik (may Allaah be pleased with him) said: The Prophet the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Eat suhoor for in suhoor there is blessing.” (Narrated by al-Bukhaari, 1923; Muslim, 1059). 

3 – It is Sunnah to delay suhoor because of the report narrated by al-Bukhaari from Anas from Zayd ibn Thaabit (may Allaah be pleased with him) who said: “We ate suhoor with the Messenger of Allaah (peace and blessings of Allaah be upon him), then he got up to pray.” I said: “How much time was there between the adhaan and suhoor?” He said: “The time it takes to recite fifty verses.” (Narrated by al-Bukhaari, 1921). 

4 – It is Sunnah to hasten to break the fast because the Prophet (peace and blessings of Allaah be upon him) said: “The people will continue to be fine so long as they hasten to break the fast.” (Narrated by al-Bukhaari, 1957; Muslim, 1098). See also question no. 49716) 

5 – It is Sunnah to break the fast with fresh dates; if none are available then with dry dates; if none are available then with water – because of the hadeeth of Anas (may Allaah be pleased with him) who said: The Messenger of Allaah (peace and blessings of Allaah be upon him) used to break his fast with fresh dates before praying; if there were no (fresh dates) then with dry dates, and if there were no (dried dates) then he would take a few sips of water.

(Nararted by Abu Dawood, no. 2356; al-Tirmidhi, 696; classed as hasan in al-Irwa’, 4/45) 

6 – It is Sunnah when breaking the fast to say what is narrated in the hadeeth, which is to say Bismillaah. This is obligatory according to the correct view because the Prophet (peace and blessings of Allaah be upon him) enjoined that.

The words “Allaahumma laka sumtu wa ‘ala rizqika aftartu, Allaahumma taqabbal minni, innaka antaal-samee’ al-‘aleem (O Allaah, for You I have fasted and with Your provision I have broken my fast, O Allaah accept (this fast) from me for You are the All-Hearing, All-Knowing) are da’eef (weak), as stated by Ibn al-Qayyim (Zaad al-Ma’aad, 2/51). 

There is also another report: “Dhahaba al-‘zama’ wa abtallat al-‘urooq wa thabata al-ajr in sha Allaah (the thirst is gone, the veins have been moistened and the reward is assured, if Allaah wills).” (Narrated by Abu Dawood, 2357; al-Bayhaqi, 4/239; classed as hasan in al-Irwa’, 4/39). 

There are ahaadeeth which speak of the virtue of the du’aa’ of the fasting person, such as the following: 

(i)                It was narrated from Anas (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “Three prayers are not rejected: the prayer of a father, the prayer of a fasting person, and the prayer of a traveler.” Narrated by al-Bayhaqi, 3/345; classed as saheeh by al-Albaani in al-Saheeh 1797. 

(ii)              It was narrated from Abu Umaamah in a marfoo’ report: “Every time the fast is broken Allaah has people whom He ransoms.” Narrated by Ahmad, 21698; classed as saheeh by al-Albaani in Saheeh al-Targheeb, 1/491. 

(iii)            It was narrated from Abu Sa’eed al-Khudri in a marfoo’ report: “Allaah ransoms people every day and night – i.e., in Ramadaan – and every day and night the Muslim has a prayer that is answered.” Narrated by al-Bazzaar; classed as saheeh by al-Albaani in Saheeh al-Targheeb, 1/491.