If a homes electricity goes out for 2-3 hours during the summer time, parents won’t be concerned about themselves getting heat-sick; they won’t be distraught by their own sweat and frustration with the heat. But when a mother sees her child restless, finding it difficult to sleep due to the extreme heat, her heart burns in despair.
Now imagine the events on the afternoon of Ashura (tenth day of Muharram) in the camps of Imam Hussain (as), his family and companions, under the scorching heat, all so thirsty. For this little infant some abstained from drinking out of the remaining water supply, in that scorching heat. Certainly they weren’t thinking about themselves when they watched little Ali Asghar.

I assume the main reason Imam Hussain (as) brought Ali Asghar to the enemy’s army, to ask for water in order to nourish the infant—while there was very little hope that these lupine enemies would have sympathy and give the baby water– was that Imam Hussain (as) had no other option and there was nothing he could do to help. When the Imam (as) moved about the tents, he noticed the air was filled with anguish and much commotion, this small infant’s thirst, hunger and distress had moved everyone. Hussain Ibn Ali (as) had to take the baby in his arms—although there was very little chance the enemy would give the baby a cup of water to sooth his thirst.
Nevertheless, Hussain Ibn Ali (as) held the infant, then lifted him up for all to see. The baby’s conditions were so heart-rending that he would certainly move anyone—no matter how cold hearted—to feel sadness for him.
Imam Hussain (as) sought mercy purposely. It has been narrated correctly that he said, “even if you don’t have mercy towards me, have mercy towards this little baby.” A father would do so for his little baby at a time of distress. Hussain Ibn Ali’s (as) fatherly instincts allowed him to ask the enemy for water in order to save the life of this little infant. At that moment Hussain Ibn Ali (as)—probably in agony, gloom, and distress—raised the baby in his hands and was talking to the enemy when he felt something strange! He noticed his baby, who was drooping and still, due to thirst and hunger, could no longer hold his head, his head hung to one side. Suddenly he started floundering in his father’s hands.
Imam Hussain (as) looked at him; he saw the enemy’s arrow had stricken the baby in the throat and blood was flowing from Ali Asghar’s throat. May God curse the oppressors!

Ayatollah Khamenei; September 12, 1986