Whenever Messenger of Allah ﷺ intended to lead a Ghazwa, he would use an equivocation from which one would understand that he was going to a different destination .  

عَنْ رَسُولِ اللَّهِ ﷺ وَلَمْ يَكُنْ رَسُولُ اللَّهِ ﷺ يُرِيدُ غَزْوَةً إِلاَّ وَرَّى بِغَيْرِهَا  

Whenever Messenger of Allah 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 Messenger of Allah 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.  

سَمِعْتُ كَعْبَ بْنَ مَالِكٍ ؓ يَقُولُ كَانَ رَسُولُ اللَّهِ ﷺ قَلَّمَا يُرِيدُ غَزْوَةً يَغْزُوهَا إِلاَّ وَرَّى بِغَيْرِهَا حَتَّى كَانَتْ غَزْوَةُ تَبُوكَ فَغَزَاهَا رَسُولُ اللَّهِ ﷺ فِي حَرٍّ شَدِيدٍ وَاسْتَقْبَلَ سَفَرًا بَعِيدًا وَمَفَازًا وَاسْتَقْبَلَ غَزْوَ عَدُوٍّ كَثِيرٍ فَجَلَّى لِلْمُسْلِمِينَ أَمْرَهُمْ لِيَتَأَهَّبُوا أُهْبَةَ عَدُوِّهِمْ وَأَخْبَرَهُمْ بِوَجْهِهِ الَّذِي يُرِيدُ  

"Scarcely did Messenger of Allah ﷺ set out for a journey on a day other than Thursday."  

أَنَّ كَعْبَ بْنَ مَالِكٍ ؓ كَانَ يَقُولُ لَقَلَّمَا كَانَ رَسُولُ اللَّهِ ﷺ يَخْرُجُ إِذَا خَرَجَ فِي سَفَرٍ إِلاَّ يَوْمَ الْخَمِيسِ  

The Prophet ﷺ set out on Thursday for the Ghazwa of Tabuk and he used to prefer to set out (i.e. travel) on Thursdays.  

أَنَّ النَّبِيَّ ﷺ خَرَجَ يَوْمَ الْخَمِيسِ فِي غَزْوَةِ تَبُوكَ وَكَانَ يُحِبُّ أَنْ يَخْرُجَ يَوْمَ الْخَمِيسِ