All of the fasts throughout the year can fall out on Shabbat, except for Asara B’Tebet. When that happens, the fast is postponed to Sunday, except for Yom Kippur, which is observed on Shabbat. On the other hand, the other fasts cannot fall on a Friday, except for Asara B’Tebet, which is observed on that day into Shabbat.
Som Gedaliah, as well as Asara b’Tebet and Shiva Asar B’Tamuz, begin at Alot Hashachar (dawn). The Shulhan Aruch rules that if one stipulated before he went to sleep the previous night that he intends to wake up and eat before the fast begins, he may do so. According to Maran, this condition is necessary even if one only wants to wake up and drink, not to eat. The Rema is lenient with regard to drinking and does not require an explicit stipulation. The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Re’eh, rules in accordance with the Shulhan Aruch.
Hacham Bension in Or Lesion Vol.3 31:2 rules that if a person accepts upon himself a personal fast, he may stipulate to eat before dawn in his thought alone. However, for a Ta’anit Sibbur (public fast), such as Som Gedaliah, he must verbally articulate the condition.
SUMMARY
If someone wants to eat or drink before dawn on a fast day, he must verbally stipulate that he intends to do so the previous night, before going to sleep.
