Verses with the word horseback in the Old Testament (5 verses):

2 Kings 9:18
So there went one on horseback to meet him, and said, Thus saith the king, Is it peace? And Jehu said, What hast thou to do with peace? turn thee behind me. And the watchman told, saying, The messenger came to them, but he cometh not again.

2 Kings 9:19
Then he sent out a second on horseback, which came to them, and said, Thus saith the king, Is it peace? And Jehu answered, What hast thou to do with peace? turn thee behind me.

Esther 6:9
And let this apparel and horse be delivered to the hand of one of the king's most noble princes, that they may array the man withal whom the king delighteth to honour, and bring him on horseback through the street of the city, and proclaim before him, Thus shall it be done to the man whom the king delighteth to honour.

Esther 6:11
Then took Haman the apparel and the horse, and arrayed Mordecai, and brought him on horseback through the street of the city, and proclaimed before him, Thus shall it be done unto the man whom the king delighteth to honour.

Esther 8:10
And he wrote in the king Ahasuerus' name, and sealed it with the king's ring, and sent letters by posts on horseback, and riders on mules, camels, and young dromedaries: