(Count ye the slaking of a pilgrim's thirst and tendance of the Inviolable Place of Worship as (equal to the worth of) him who believeth in Allah) [9:19].
Abu Ishaq al-Tha'alibi, may Allah have mercy on him, informed us> 'Abd Allah ibn Hamid al-Wazzan> Ahmad ibn Muhammad ibn Ja'far> ibn 'Abd Allah al-Munadi> Abu Dawud Sulayman ibn al-Ash'ath> Abu Tubah al-Rabi' ibn Nafi' al-Halabi> Mu'awiyah ibn Salam> Zayd ibn Salam> Abu Salam> al-Nu'man ibn Bashir who said: “I was sitting close to the pulpit of the Messenger of Allah, Allah bless him and give him peace, when a man said: 'I do not care if I ever do any other good works after I quench the thirst of the pilgrims', another man said: 'I do not care if I ever do any other work after tending to the Sacred Mosque', and a third man said: 'Jihad in the way of Allah is much better than what you have mentioned'. 'Umar ibn al-Khattab rebuked them, saying: 'Do not raise your voices so close to the pulpit of the Messenger of Allah, Allah bless him and give him peace, (this happened to be a Friday). But what I will do is that, after performing my prayer, I will go in and ask the verdict of the Messenger of Allah, Allah bless him and give him peace, concerning that about which you have differed'. He did, and then Allah, exalted is He, revealed (Count ye the slaking of a pilgrim's thirst and tendance of the Inviolable Place of Worship) up to His words (Allah guideth not wrongdoing folk…)”. This was narrated by Muslim from al-Hasan ibn 'Ali al-Halwani from Abu Tubah.
Said Ibn 'Abbas, according to the report of al-Walibi: “When he was taken prisoner on the Day of Badr, al-'Abbas ibn 'Abd al-Muttalib said: 'If you have precedence over us through Islam, migration and Jihad, we also used to tend to the Sacred Mosque, quench the thirst of the pilgrims and relieve the afflicted'. Allah, exalted is He, revealed therefore (Count ye the slaking of a pilgrim's thirst and tendance of the Inviolable Place of Worship…)”.
Al-Hasan, al-Sha'bi and al-Qurazi said: “This verse was revealed about 'Ali, al-'Abbas and Talhah ibn Shaybah who boasted to each other. Talhah said: 'I am the master of the House, its key is in my hand. I could sleep inside it if I wanted to and the apparel of its house belongs to me'. Al-'Abbas said: 'I am in charge of providing water to the pilgrims'. 'Ali said: 'I do not know what you are talking about, I have prayed six months before anybody else and I have taken part in Jihad'. And so Allah, exalted is, revealed this verse”.
Ibn Sirin and Murrah al-Hamadani said: “'Ali [ibn Abi Talib] said to al-'Abbas [ibn 'Abd al-Muttalib]: 'Are you not going to migrate to join the Prophet, Allah bless him and give him peace?' al-'Abbas said: 'Am I not doing something much better than migration? Do I not quench the thirst of the pilgrims to the House of Allah and tend to the Sacred Mosque?' And so, this verse was revealed as were revealed Allah's words (Those who believe, and have left their homes and striven with their wealth and their lives…) [9:20]”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou