That poetry was made by order of the Prophet (SAWA) to register and confirm in the memory of people the great declaration of Ghadeer. The poetry of Hassaan Ibn Thaabit
يناديهم يوم الغدير نبيهم
بخمّ وأكرم بالنبي مناديا
Has become one of the important poetry in the history of Islam which recorded the most important order of the Prophet Muhammad (SAWA).