Hadith: Indeed, Allah, the Almighty,, has added a prayer for you, so offer it in the period between ‘Ishā' prayer and Fajr prayer; (it is) the Witr, (it is) the Witr

عن أبي تَمِيم الجَيْشَانِيِّ قال: سمعت عمرو بن العَاص يقول: أخبرني رَجُل من أصحاب النبي صلى الله عليه وسلم يقول: إن رسول الله صلى الله عليه وسلم قال: «إن الله عز وجل زَادَكُمْ صلاة فصلُّوها فيما بَيْن صلاة العِشَاء إلى صلاة الصُّبح، الوِتر الوِتر»، أَلَا وإنَّه أبو بَصْرَة الغِفَاري، قال أبو تَميم: فكنت أنا وأبو ذَرٍ قاعِدَين، قال: فأخذ بِيَدِي أبو ذَرٍّ فانطلقنا إلى أبي بَصْرة فوجدناه عند الباب الذي يَلِي دار عَمرو بن العاص، فقال أبو ذَرٍّ: يا أبا بَصْرَة آنت سمعت النبي صلى الله عليه وسلم يقول: «إن الله عز وجل زَادَكُمْ صلاة، فصلُّوها فيما بَيْن صلاة العشاء إلى صلاة الصُّبح الوِتر الوِتر؟» قال: نعم، قال: أنْتَ سَمِعْتَه؟ قال: نعم، قال: أنت سمعته؟ قال: نعم.
[صحيح] - [رواه أحمد]

Abu Tamīm al-Jayshāni reported: I heard ‘Amr ibn al-‘Ās say: "A man from the Companions of the Prophet (may Allah's peace and blessings be upon him) informed me that the Messenger of Allah (may Allah's peace and blessings be upon him) said: 'Indeed, Allah, the Almighty, has added a prayer for you, so offer it in the period between the ‘Ishā' prayer and the Fajr prayer; (it is) the Witr, (it is) the Witr.' Behold, this Companion was Abu Basrah al-Ghifāri." Abu Tamīm said: "Abu Dharr and I were sitting, so Abu Dharr took me by the hand and we set off to Abu Basrah. We found him at the door next to the house of ‘Amr ibn al-‘Ās. Abu Dharr said: 'O Abu Basrah, did you hear the Prophet (may Allah's peace and blessings be upon him) say: 'Indeed, Allah, the Almighty, has added a prayer for you, so offer it in the period between the ‘Ishā' prayer and the Fajr prayer; (it is) the Witr, (it is) the Witr?' He replied: 'Yes.' Abu Dharr asked: 'You heard him?' He replied: 'Yes.' He asked again: 'You heard him?' He replied: 'Yes.'"
[Authentic hadith] - [Narrated by Ahmad]

Explanation

"Allah, the Almighty, has added a prayer for you": Allah added for them another prayer that they did not offer before in this manner, which is the Witr prayer. The statement indicates that Allah added that prayer as a favor to Muslims, as if he was saying: Allah has made the five prayers obligatory upon you so as to reward you for them, but He did not settle for that; rather, He prescribed for you voluntary night prayer and Witr in order to extend to you more favor. "So offer it": this is a command. As a basic rule, a command implies obligation; however, this Hadīth as well as others whose apparent meaning is that the "Witr" prayer is obligatory were construed to mean that it is recommended, not obligatory, based on authentic explicit evidence. "in the period between ‘Ishā' prayer and Fajr prayer": this part specifies the time frame for offering Witr, which begins after performing ‘Ishā' prayer. So, when a person finishes offering the ‘Ishā' prayer, the time for Witr prayer starts, even if he offers ‘Ishā combined with Maghrib in advance (at the time of Maghrib). The time to offer Witr ends at the break of dawn; i.e. when the time of the Fajr prayer starts. If dawn breaks while one is offering Witr, he should complete it. Then ‘Amr ibn al-‘Ās (may Allah be pleased with him) said: "and behold, this person was Abu Basrah al-Ghifāri," i.e. the one who informed ‘Amr ibn al-‘Ās was Abu Basrah al-Ghifāri (may Allah be pleased with him)." Abu Tamīm said: "Abu Dharr and I were sitting. So Abu Dharr took me by the hand and we set off to Abu Basrah. We found him at the door next to the house of ‘Amr ibn al-‘Ās," i.e. that after they were informed of that statement of the Messenger of Allah (may Allah's peace and blessings be upon him) they wanted to confirm its accuracy. So, they went to Abu Basrah (may Allah be pleased with him) and when they reached him, Abu Dharr asked him about the authenticity of the statement he reported from the Prophet (may Allah's peace and blessings be upon him). "He replied: 'Yes.' Abu Dharr asked: 'You heard him?' He replied: 'Yes.' He asked again: 'You heard him?' He replied: 'Yes.'" So he confirmed to them that the statement that he reported from the Prophet (may Allah's peace and blessings be upon him): "Indeed, Allah, the Almighty, has added for you a prayer…" was authentic