In 8 A.H., Muhammad ﷺ despatched towards the sea-shore an expedition of three hundred(300) men, under the command of Abu Ubaidah bin Al-Jarrah(RA). Their mission was to watch the caravan of the Quraish pagans(tribe of Juhaynah at al-Khabat) near the Red Sea. He ﷺ gave them a bag full of dates for their rations.
 Jabir b. ‘Abdullah reported:
Allah’s Messenger (may peace he upon him) sent us (on an expedition). We were three hundred riders and our chief (leader) was 'Ubaida b. al-Jarrah. We were on the look out for a caravan of the Quraish. So we stayed on the coast for half a month, and were so much afflicted by extreme hunger that we (were obliged) to eat leaves. That is why it was called the Detachment of the Leaves. The ocean cast out for us an animal which was called al-'Anbar (whale). We ate of that for half of the month and rubbed its fat on our (bodies) until our bodies became stout. Abu 'Ubaida caught hold of one of its ribs and fixed that up. He then cast a glance at the tallest man of the army and the highest of the camels. and then made him ride over that, and that-tnan passed beneath it (the rib), and many a man could sit in its eye-socket, and we extracted many pitchers of fat from the cavity of its eye. We had small bags containing dates with us (before finding the whale). 'Ubaida gave every person amongst us a handful of dates (and when the provision ran short), he then gave each one of us one date. And when that (stock) was exhausted, we felt its loss.
 Allah’s Apostle sent an army towards the east coast and appointed Abu 'Ubaida bin Al-Jarrah as their chief, and the army consisted of three-hundred men including myself. We marched on till we reached a place where our food was about to finish. Abu- 'Ubaida ordered us to collect all the journey food and it was collected. My (our) journey food was dates. Abu 'Ubaida kept on giving us our daily ration in small amounts from it, till it was exhausted. The share of everyone of us used to be one date only.“ I said, "How could one date benefit you?” Jabir replied, “We came to know its value when even that too finished.” Jabir added, “When we reached the sea-shore, we saw a huge fish which was like a small mountain. The army ate from it for eighteen days. Then Abu 'Ubaida ordered that two of its ribs be fixed and they were fixed in the ground. Then he ordered that a she-camel be ridden and it passed under the two ribs (forming an arch) without touching them.”
When they reached the verge of starvation, Allāh had mercy on them for He always brings ease after every hardship, provided it is endured patiently.
A big fish known as Al-’Anbar was thrown out of the sea for them. The Sahabah(RA) reported that it was like a small mountain. The fish was so big that they all lived on it for eighteen days and rubbed its fat on their bodies till they returned to their original state of being strong and healthy.
Abu Ubaida(RA) ordered two of its ribs to be fixed on the ground; then he went to the tallest man of his companions, and got him to ride on his she-camel under this arch formed by the two ribs. Another narration said that eighteen Sahabah(RA) could stand in the eye socket alone!
They also filled their satchels with the remaining portion, which lasted them right up to Madinah. When the episode was narrated to Muhammad ﷺ, he said: “The fish was a provision arranged for you by Allah, feed us if you have some of it.” He was given some of the fish and he ate it.
This army came to be known as Jaish-ul-Khabt for they ate the Khabt, the leaves of the Salam, a thorny desert, by moistening it by water.
This expedition is famous because Muslims were short of supply and food was running out, and they were fighting for survival, they suffered from famine, but in the end, the Muslims were given Mercy from Allah.
The trial of a person is proportionate to his position near Allāh, and He bestows solace and comfort by His Grace and Mercy after each trial.
Muhammad ﷺ said;
“The worst trials in this world are reserved for the Prophets, then for those who are next to them, and then for those who are best of the rest.”
Look how much the Sahābah have suffered in the path of Allāh. They had live on leaves of trees, starve and shed blood in the service of the true faith, which we now fail to preserve.
Sources: Hikayaat-e-Sahabāh Chapter 3: Abstinence and Self-Denial of the Sahabah
 Sahih Muslim, 21:4757  Sahih al-Bukhari, 3:44:663