It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that when rain would descend, he would say: O girl! Put my saddle and clothes outside, and he would say: (The command of Allah, the Exalted, is): "And We sent down blessed water from the sky." [سورہ ق: 9]
Benefits and Issues: It has already been mentioned in the previous pages under Hadith 571 that when it rained, the Prophet (sallallahu alayhi wa sallam) would remove his shirt or similar garment so that the rain would fall directly on his body. The noble Companions (radi Allahu anhum) said: We asked, "Why do you do this?" He replied: "Because it has just come freshly from its Lord." Sayyiduna Ibn Abbas (radi Allahu anhuma) would also do this in following the Prophet (sallallahu alayhi wa sallam). Therefore, the water of rain is blessed. One may seek blessing (tabarruk) from it.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 1228