The Quran

لَقَد صَدَقَ اللَّهُ رَسولَهُ الرُّؤيا بِالحَقِّ ۖ لَتَدخُلُنَّ المَسجِدَ الحَرامَ إِن شاءَ اللَّهُ آمِنينَ مُحَلِّقينَ رُءوسَكُم وَمُقَصِّرينَ لا تَخافونَ ۖ فَعَلِمَ ما لَم تَعلَموا فَجَعَلَ مِن دونِ ذٰلِكَ فَتحًا قَريبًا

Muhammad Asad

Indeed, God has shown the truth in His Apostle's true vision:¹ most certainly shall you enter the Inviolable House of Worship, if God so wills, in full security, with your heads shaved or your hair cut short,² without any fear: for He has [always] known that which you yourselves could not know.³ And He has ordained [for you], besides this, a victory soon to come.⁴

Shortly before the expedition which ended at Hudaybiyyah, the Prophet had a dream in which he saw himself and his followers entering Mecca as pilgrims. This dream-vision was destined to be fulfilled a year later, in 7 H., when the Muslims were able to perform their first peaceful pilgrimage to the Holy City.
Male pilgrims usually shave or (which is the meaning of the conjunctive wa in this context) cut their hair short before assuming the pilgrim's garb (ihram), for it is not permitted to do so while in the state of pilgrimage. A repetition of the same act marks the completion of the pilgrimage (cf. 2:196).
Namely, the future.
See note 22.