Sahih al-Bukhari 2948Book 56, Hadith 160
وَحَدَّثَنِي أَحْمَدُ بْنُ مُحَمَّدٍ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ بْنِ كَعْبِ بْنِ مَالِكٍ، قَالَ سَمِعْتُ كَعْبَ بْنَ مَالِكٍ ـ رضى الله عنه ـ يَقُولُ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم قَلَّمَا يُرِيدُ غَزْوَةً يَغْزُوهَا إِلاَّ وَرَّى بِغَيْرِهَا، حَتَّى كَانَتْ غَزْوَةُ تَبُوكَ، فَغَزَاهَا رَسُولُ اللَّهِ صلى الله عليه وسلم فِي حَرٍّ شَدِيدٍ، وَاسْتَقْبَلَ سَفَرًا بَعِيدًا وَمَفَازًا، وَاسْتَقْبَلَ غَزْوَ عَدُوٍّ كَثِيرٍ، فَجَلَّى لِلْمُسْلِمِينَ أَمْرَهُمْ، لِيَتَأَهَّبُوا أُهْبَةَ عَدُوِّهِمْ، وَأَخْبَرَهُمْ بِوَجْهِهِ الَّذِي يُرِيدُ.
Whenever Allah's Messenger (ﷺ) intended to carry out a Ghazwa, he would use an equivocation to conceal his real destination till it was the Ghazwa of Tabuk which Allah's Messenger (ﷺ) carried out in very hot weather. As he was going to face a very long journey through a wasteland and was to meet and attack a large number of enemies. So, he made the situation clear to the Muslims so that they might prepare themselves accordingly and get ready to conquer their enemy. The Prophet (ﷺ) informed them of the destination he was heading for.