We all know about the Muhajirun and the Ansar. But do you know there was another category, the Muhajirun Ansariyun, i.e. the Immigrant Ansar?
Muhammad b. Sa‘d al-Baghdadi (d. 230/785) mentioned in his al-Tabaqat al-Kabir;
فلما قدم أول من هاجر إلى قباء خرجوا إلى رسول الله، صلى الله عليه وسلم، بمكة حتى قدموا مع أصحابه في الهجرة، فهم مهاجرون أنصاريون، وهم: ذكوان بن عبد قيس، وعقبة بن وهب بن كلدة، والعباس بن عبادة بن نضلة، وزياد بن لبيد
After the first batch of immigrants had reached Quba, some of them (Ansar) came to Makkah and then migrated with the companions; they are known as Muhajirun Ansariyun (the Immigrant Ansar). Their names are Dhakwan Ibn ‘Abd Qays, ‘Uqbah Ibn Wahb Ibn Kaldah, al-‘Abbas Ibn ‘Ubadah Ibn Nadhlah and Ziyad Ibn Labid.
They belonged to Madinah and had come to Makkah to return to al-Madinah as Muhajirs so that they might get the reward of Hijrah, i.e. making immigration in the way of Allah.
May Allah accept their great deed and bless them with the reward they sought.
 Ibn Sa‘d, Muhammad, al-Tabaqat al-Kabir, (Beirut: DKI, 1990) Vol.1, 175; translated in Ibn Sa‘d’s Kitab al-Tabaqat al-Kabir, English Translation by S. Moinul Haq (New Delhi: Kitab Bhavan Publishers, 2009) Vol.1, 262; it was also quoted in Sibt Ibn al-Jawzi, Yusuf ibn Qizoghlu, Mir’at al-Zaman fi Tawarikh al-A‘yan, (Damascus: Dar al-Resalah, 2013) Vol.3, 159