Some scholars’ say this is the second Badr, which happened in the year 4 Hijri. But there are enough evidences to say that this is the third Badr.
After the battle of Uhud, Abu Sufyan told the Muslims that they will come to Badr the following year and fight them. So when time passed, and was coming near to the date the Quraysh set, the Muslims got ready to engage the enemy. Although the Quraysh promised to fight the Muslims on this date, they changed their minds. But it didn’t take long after this, they set out with many tribes in Arabia against the Muslims, called the battle of Khandaq.
Historical reports on this incident
Kitab al-Tabaqat al-kabir – Ibn Sa’d:
GHAZWAH OF THE APOSTLE OF ALLAH, … TO BADR AL-MAW’ID
Then (occurred) the ghazwah Badr al-Mawa’id of the Apostle of Allah, and that is different from the ghazwah of Badr al-Qital (in which fighting took place). It was on the (appearance of the) crescent of Dhu al-Qa’dah, after the commencement of the forty-fifth month from his Hijrah.
They Said: When Abu Sufyan Ibn Harb wanted to return from the battle of Uhud; he cried: There will be a recurrence (of fighting) between you and us in the beginning of next year at Badr al-Safra, where we will fight. … Then the people dispersed and the Quraysh returned. They (Quraysh) informed their allies of the possible recurrence and made arrangement for marching out. When the period came to a close, Abu Sufyan was reluctant to march. (In the meantime) Nu’aym Ibn Mas’ud al-Ashja’I arrived in Makkah, Abu Sufyan said to him: I made a promise to confront Muhammad and his companions at Badr. That time has come, but this is a year of drought while a year of plenitude and prosperity suits us. …
We will carry out twenty of your assignments for which Suhayl Ibn Amr will be a surety, only you will have to go al-Madinah and induce the Companions of Muhammad to desert him. He said: Yes. They (Quraysh) made arrangements and made him ride a came. He travelled fast and arrived at al-Madinah. He informed them of Abu Sufyan’s mobilization (of forces) and of what he had of plenty of arms and equipments. The Apostle of Allah, Said: By him in Whose hand is my Soul! I shall surely march even if a single person does not accompany me.
Allah helped the Muslims and dread went out (of their hearts). The Apostle of Allah, appointed Abd’Allah Ibn Rawahah as his vicegerent at al-Madinah. Ali Ibn Abi Talib was his standard-bearer; he (Prophet), marched with one thousand and five hundred Muslims. There were only ten horses. They set out with their merchandise. Badr al-safra was a place of assembling of the Arabs and a market was held there from the crescent (first day) of Dhu al-Qa’adah toll the eighth and then people dispersed to their houses. They (Muslims) reached Badr on the first night of Dhu al-Qa’dah and the market commenced the next morning. There they stayed for eight days and sold what merchandise they had brought and made a profit of a dirham for a dirham (i.e., 100 p.c.) and returned. The Prople heard about their march. Abu Sufyan Ibn Harb set out from Makkah with two thousand men of the Quraysh and fifty horses.
They reached Majannaj, which was also known as Marr al-Zahran; he said: return. Verily, a year of plenty and prosperity suits us when we graze (our animals under the shade) of trees and drink milk. This year is the year of drought. I am going back and you should also return. The people of Makkah called this army, the army of al-Sawiq (gruel of parched barley). They say: They had come out drinking gruel of parched barley. Ma’bad Ibn Abu Ma’bad al-Khuza’I came to Makkah with the news of the Apostle of Allah, and his march to Badr with his companions. Thereupon Safwan Ibn Umayyah said to Abu Sufyan: I stopped you that day from (threatening them) by fixing a period; now they are emboldened as they have noticed that we stayed behind. Then they began preparations for the Ghazwah of Khandaq (Ditch). 
THE LAST EXPEDITION TO BADR, A.H. 4
In Sha’ban he went forth to Badr to keep his appointment with Abu Sufyan and stopped there. He stayed there for eight nights waiting for Abu Sufyan. Abu Sufyan with the men of Mecca went as far as Majanna in the area of (T. Murr) al-Zahran. Some people say he reached (T. passed through) Usfan; then he decided to go back. He told the Quraysh that the only suitable year was a fertile year when they could pasture the animals on the herbage and drink their milk, whereas this was a dry year. He was going to return and they must return with him. And so they did. The Meccans called them ‘the porridge army’, saying that they merely went out to drink porridge. …As he remained waiting for Abu Sufyan, Ma’bad b. Abu Ma’bad al-Khuza’I passed by. He had seen where the Apostle was as his she-camel passed swiftly. … 
Scholars commenting on this incident
Abu Sufyan was not eager to fulfil the promise he had made when leaving Uhud. He left Makkah with a heavy heart, thinking of the consequences of fighting the Muslims, and, as yet, he had not made sufficient preparations as he would have liked. His people had been defeated at Badr in spite of their superior numbers and equipment, and they barely managed gain victory at Uhud after almost being defeated. If it had not been for the error made by the army of Allah, the Quraish would not have made any gains in the battle. Thus Abu Sufyan had hardly reached Dhahran when it occurred to him to make a retreat, and he shouted to his men:
‘O people of the Quraish, only a year of fertility will be beneficial for you. In which you grow trees and drink milk. However, this year is a barren year and I am going back, so you go back too.’
Thus did the Quraish withdraw from the expected battle. The Muslims, however, mobilized themselves for the encounter with the Quraish with all fervour. They reached the wells of Badr and camped around them, announcing the fulfilment of their word and their readiness for the promised fight. For eight days they remained waiting for the approach of the Quraish, emoving the last specks of mud which Uhud had thrown at their reputation. That was in Sha’ban of the fourth year after the Hijrah. 
Maulana Muhammad Ali:
Departing from Uhud, the Quraish had thrown out a challenge to the Muslims, that their fate would be tried again at Badr, the following year. Accordingly, when the time came, the Muslims marched to Badr but, not finding the Quraish there, peacefully returned, after disposing at the fair annually held there of whatever merchandise they had taken with them. 
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 Kitan al-Tabaqat al-kabir, by Ibn Sa’d, page 71 – 73
 Ibn Ishaq’s Sirat Rasul Allah – The Life of Muhammad [Translated by A. Guillaume], page 447
 Muhammad Al-Ghazali, Fiqh-us-seerah, page 311 – 312
 Muhammad the Prophet By Maulana Muhammad Ali, 107