What is the Hijrah? Why does the Islamic calendar start there?

"Muhajirun of Quraysh. His migration occurred a year before the pledge of Al-Aqaba after facing harm from Quraysh upon his return from Abyssinia. He resolved to return to Al-Medina knowing he had brothers there. Ibn Ishaq narrated from Umm Salama who recounted her journey to Medina. When her husband Abu Salama decided to leave for Medina, he prepared their camel, placed her on it with their son Salama in her lap and set off. However, the men of Banu al-Mughirah stopped them, taking her away and seizing the camel. The sons of Abd al-Assad, Abu Salama's clan, were angered and took the child Salama from her resulting in his arm being dislocated. Abu Salama continued to Medina"

"those who sought refuge with them. The Messenger of Allah, peace be upon him, instructed his companions from the Muhajirun and those in Makkah to migrate to Al-Medina and join their brothers from the Ansar. He assured them, Indeed, Allah has made for you brothers and a home in which you will be safe. They began their migration in groups while the Messenger of Allah remained in Makkah awaiting permission from his Lord to leave. The first to migrate to Al-Medina from the companions of the Messenger of Allah, peace be upon him, was Abu Salama Abdullah Ibn Abd al-Assad from the Muhajirun of Quraysh. His migration occurred a year before the pledge of Al-Aqaba after facing harm"

"of Trustworthy and Weak Narrators. All praise and gratitude belong to Allah. Chapter. In the first year of the Hijra, Abdullah ibn al-Zubayr was born. He was the first child born in Islam after the Hijra. This is narrated by al-Bukhari from his mother, Asma, and his aunt, Aisha, the mother of the believers. May Allah be pleased with them both. Some say that Numan ibn Bashir was born six months before him, making Abdullah ibn al-Zubayr the first child born among the emigrants after the Hijra. Others claim both were born in the second year of the Hijra, but the first claim seems more accurate. All praise belongs to Allah and"

"of Ibrahim, then from the construction of the Kaaba by Ibrahim and Ismail, then from the death of Ka'b ibn Lu'ayy, and then from the year of the elephant. Finally, Umar ibn al-Khattab established the calendar from the Hijra, which was in the year 17 or 18. The point is that they established the beginning of the Islamic calendar from the year of the Hijra, and they made its first month Muharram, as is widely known among them, and this is the opinion of the majority of the scholars."

"I heard the Messenger of Allah, peace and blessings be upon him and his family, say, Indeed, actions are judged by intentions, and every person will have what they intended. So whoever's migration is for Allah and His Messenger, then their migration is for Allah and His Messenger. And whoever's migration is for worldly gain they hope to achieve, or for a woman they wish to marry, then their migration is for that which they migrated towards."

"The meaning is: Whoever repents to اللّٰه with intention, resolve, and determination, his repentance to اللّٰه is through action and deed. This is similar to the saying of the Prophet, peace be upon him: "Whoever's migration is for اللّٰه and His Messenger, then his migration is for اللّٰه and His Messenger. And whoever's migration is for worldly gain or a woman to marry, then his migration is to what he migrated for.""

"Our scholars and others have differed in the meaning of no migration after the conquest. Some say it means no migration from Mecca since it became the abode of Islam. Others interpret it as no migration after the conquest with complete merit. As for migration from the abode of disbelievers today, it is emphatically obligatory for those who are unable to manifest the religion of Islam there."

"In this regard, the Prophet, peace be upon him, said: "Actions are but by intentions, and for each person is what he intended. So whoever's migration was to Allah and His Messenger, his migration is to Allah and His Messenger, and whoever's migration was for worldly gains or to marry a woman, his migration is for what he migrated to.""

"trees, hoping it was the town my companion had described, but it did not settle in my heart. While I was with him, a cousin of his from Banu Qurayza came from Al-Madinah, bought me, and took me to Al-Madinah. By Allah, it wasn't long before I saw it and recognized it by the description of my companion. I stayed there, and the Messenger of Allah, peace be upon him, was sent and remained in Makkah for as long as he did. I did not hear anything of him due to my work as a slave. Then he migrated to Al-Madinah, and by Allah, I was at the top of a date palm belonging to my master, doing some work. My master was sitting"

"it is also reported from Aisha may Allah be pleased with her through a different chain another hadith Muawiyah Ibn Abi Sufyan during a pilgrimage addressed the people of Medina he held a piece of hair and said Oh people of Medina where are your scholars I heard the messenger of Allah peace be upon him forbidding such things and saying the children of Israel perished when their women took to them this hadith is considered authentic and was narrated by several scholars including Al-Tirmidhi Muawiyah Ibn Abi Sufyan during his last visit to Medina addressed the people pulling out a tuft of hair and saying I"