He had already clarified that they would shave their heads at Hudaybiyyah itself and would return to Madinah Munawwarah without reaching Makkah Mukarramah.

It is narrated from Sayyiduna Ka'b bin 'Ujrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) passed by him while he was lighting a fire under a pot. At that time, lice were falling onto his face. The Noble Prophet (peace and blessings of Allah be upon him) said: "Are these lice troubling you?" He replied, "Yes, O Messenger of Allah." Then this verse was revealed «‏‏‏‏فَفِدْيَةٌ مِّن صِيَامٍ أَوْ صَدَقَةٍ أَوْ نُسُكٍ» ‏‏‏‏ [ سورة البقرة: 196 ] "(Whoever shaves his head in the state of Ihram) then he should fast, or give charity, or offer a sacrifice." Therefore, the Prophet commanded him while the Companions were still at Hudaybiyyah. And he did not tell them that they would shave their heads at Hudaybiyyah; the Companions wished that they would enter Makkah (and perform 'Umrah). So Allah the Exalted revealed the verse regarding fidyah, and the Prophet (peace and blessings of Allah be upon him) commanded Sayyiduna Ka'b bin 'Ujrah (may Allah be pleased with him): "Shave your head and fast for three days, or feed six needy people with a faraq (three sa') of grain, or slaughter a goat (and distribute it among the poor)."