From the Reuters article:

However, the Israeli military denied responsibility for the blast at the Al-Ahli al-Arabi hospital in Gaza City, suggesting the hospital was hit by a failed rocket launch by the enclave's Palestinian Islamic Jihad military group.

"An analysis of IDF operational systems indicates that a barrage of rockets was fired by terrorists in Gaza, passing in close proximity to the Al Ahli hospital in Gaza at the time it was hit."

"Intelligence from multiple sources we have in our hands indicates that Islamic Jihad is responsible for the failed rocket launch which hit the hospital in Gaza"