Yes, the Muslims should pray for their brothers in Gaza, asking Allaah to protect them and save them, and to help them against their enemy, and to defeat the Jews and those who help them. 

The imam should say the du’aa’ out loud and the people behind him should say Ameen. If a person is offering the obligatory prayer on his own, he should also say Qunoot. 

It is proven that the Prophet (blessings and peace of Allaah be upon him) said Qunoot at the time of calamity on a number of occasions: 

1.

Some of the Arab tribes betrayed 70 of the companions of the Prophet (blessings and peace of Allaah be upon him) and killed them. Anas ibn Maalik (may Allaah be pleased with him) said: News of that reached the Prophet (blessings and peace of Allaah be upon him), and he prayed Qunoot for a month, praying during Fajr prayer against some of the tribes of the Arabs, against Ri’l, Dhakwaan, ‘Usayyah and Bani Lahyaan. Narrated by al-Bukhaari (3064). 

2.

It was narrated that Anas ibn Maalik (may Allaah be pleased with him) said: Qunoot was offered in Maghrib and Fajr prayer. Narrated by al-Bukhaari (798). 

3.

It was narrated that Ibn ‘Abbaas (may Allaah be pleased with him) said: The Messenger of Allaah (blessings and peace of Allaah be upon him) prayed Qunoot for a month in Zuhr, ‘Asr, Maghrib, ‘Isha’ and Fajr prayer, when he said: Sami’a Allaahu liman hamidah in the last rak’ah, praying against some tribes of Banu Sulaym, and against Ri’l, Dhakwaan and ‘Usayyah, and those who were behind him said Ameen. Narrated by Abu Dawood (1443). Ibn al-Qayyim said: A saheeh hadeeth. Zaad al-Ma’aad, 1/280; classed as hasan by al-Albaani in Saheeh Abi Dawood, 

A number of things may be learned from these hadeeths, including the following: 

Firstly: it is prescribed to pray Qunoot at times of calamity. Ibn Taymiyah (may Allaah have mercy on him) said: Qunoot is Sunnah at the time of calamity. This view is that of the fuqaha’ among the muhadditheen. And it is narrated from the Rightly Guided Caliphs. End quote. 

Majmoo’ al-Fataawa (23/108) 

Secondly: The Prophet (blessings and peace of Allaah be upon him) said Qunoot at times of calamity in all of the five daily prayers, and he said Qunoot in Fajr and Maghrib prayer, and especially in Fajr. Ibn Taymiyah (may Allaah have mercy on him) said: Most of his Qunoot -- referring to the Prophet (blessings and peace of Allaah be upon him) -- was in Fajr. End quote. 

Majmoo’ al-Fataawa (22/269). 

Ibn al-Qayyim (may Allaah have mercy on him) said: The practice of the Prophet (blessings and peace of Allaah be upon him) was to say Qunoot especially at times of calamity, and not to do so at other times. He did not limit it only to Fajr, rather most of his Qunoot was in Fajr because it is prescribed to make that prayer lengthy. End quote. 

Zaad al-Ma’aad (1/273) 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: 

To sum up, saying Qunoot during the obligatory prayers is not prescribed either in Fajr or any other prayer, except when a calamity befalls the Muslims that is deserving of Qunoot, in which case it is prescribed to say Qunoot for every worshipper in Maghrib and Fajr prayer, and if one says Qunoot in all the prayers, there is nothing wrong with that as some of the scholars said. And when this calamity ceases, Qunoot should be stopped. End quote. 

Majmoo’ Fataawa Ibn ‘Uthaymeen (14/175) 

We ask Allaah to hasten relief for our brothers in Gaza, and to give them a way out of every difficulty and relief for every distress, and to curse and destroy the Jews and their helpers, and to send punishment upon them, for He is able to do that. 

And Allaah knows best.