Brachot 30 - One Who hears prayer
One who travels in a dangerous place can say a very short prayer. What is its text? Rabbi Yehoshua says, "Save, O God, Your nation, the remnant of Israel; at every cross-roads (meaning, even if they are crossing You) may their needs be before You. Blessed are You, God, who hears prayer." Rabbi Eliezer says, "Grant peace of mind to those who fear You; do to them what's right in Your eyes (but don't punish them through others, more than needed). Blessed are You, God, who hears prayer." Others say, "The needs of Your nation Israel are many, but their minds are limited to express them; may it be Your will to give to everyone enough for his sustenance. Blessed are You, God, who hears prayer."
If one is traveling on a donkey, and the time for Standing prayer comes, he should dismount and pray. If he cannot dismount either because of company or because there is nobody to hold the donkey, he can pray while riding, and he should turn his face towards Israel, and in Israel - towards Jerusalem, and imagine himself in the Holy of Holies.
On Shabbat, they would bring a special additional sacrifice, and correspondingly, there is an additional prayer on Shabbat, called Musaf (additional). Rabbi Elazar ben Azaryah says that it should only be said in a congregation, but the Sages says that everybody needs to recite it. Rabbi Yehudah says that if there is a congregation in his town, he can rely on them, but if not, he needs to say it himself.
Art: Camille Pissarro - The Donkey Ride at Le Roche Guyon