The Messenger of Allah ﷺ used to pray four units of prayer after the sun passed its zenith, before the noon prayer. He said, "It is an hour in which the gates of heaven are opened, and I love that a righteous deed of mine should ascend during it."
أن رسول الله ﷺ كان يصلي أربعا بعد أن تزول الشمس قبل الظهر، وقال: إنها ساعة تفتح فيها أبواب السماء، وأحب أن يصعد لي فيها عمل صالح.
Tirmidhi related it in his Sunan (478) and in Shamail (289), and Nasai in Kubra (331), all of them through Abu Dawud Tayalisi, who said, Muhammad bin Muslim bin Abu Wadah, who is Abu Saeed the tutor, narrated to us, from Abdul-Kareem Jazari, from Mujahid, from Abdullah bin Saaib, and he related it.Imam Ahmad also related it (15396) from Abu Dawud Tayalisi through the same chain, and in it, "I loved to send forth in it a righteous deed." There is no entry for Abdullah bin Saaib in Musnad Abu Dawud Tayalisi.Tirmidhi said, hasan gharib.I say, its isnad is hasan because of Muhammad bin Muslim bin Abu Wadah, for there is disagreement about him. A group of the imams of hadith deemed him reliable, though Bukhari said of him, "There is something questionable about him," but perhaps he meant by that the particular hadith he related, not that he stands at the lowest rank, as is commonly understood from Bukhari's statement. See my book, Mujam Mustalahat Hadith.This hadith indicates that it is recommended to pray four rak'ahs after the sun's decline, which is distinct from the sunnah prayer before Dhuhr.Tirmidhi said, on this subject there are also narrations from Ali and Abu Ayub.I say, as for the hadith of Ali, it was related by Ahmad, Tirmidhi, Nasai, Ibn Majah, and others, that the Prophet ﷺ used to pray four rak'ahs before Dhuhr when the sun declined, and two rak'ahs after it. It is a hasan hadith whose sourcing was given earlier in the chapter on the Prophet's ﷺ voluntary daytime prayers.As for the hadith of Abu Ayub, it was related by Abu Dawud (1270), Ibn Majah (1157), and Tirmidhi in Shamail (293), all of them through Ubayda bin Mutab Dabbi, from Ibrahim, from Sahm bin Minjab, from Qazaa, from Qurtha, from Abu Ayub, that the Prophet ﷺ used to pray four rak'ahs before Dhuhr when the sun declined, not separating between them with a taslim. And he said, "The gates of heaven open when the sun declines." Its isnad is daif, containing Ubayda bin Mutab, whom Abu Dawud and others declared daif.Munziri said, it cannot be relied upon as evidence. Ibn Khuzayma also spoke about it, saying, "As for the report that some people used as evidence for the four rak'ahs before Dhuhr, claiming that the Prophet ﷺ prayed them with a single taslim, it was related by an isnad that cannot be relied upon by anyone knowledgeable in the transmission of reports." He then related it through the chain mentioned earlier, and discussed Ubayda bin Mutab, saying among what he said, "I heard Abu Qilaba relate from Hilal bin Yahya, who said, 'I heard Yusuf bin Khalid Samti say, "I said to Ubayda bin Mutab, 'This that you narrate from Ibrahim, did you hear all of it?' He said, 'Some of it I heard, and some of it I derive by analogy.' I said, 'Then tell me what you heard, for I know analogy better than you.'"'"However, Samti was criticized by more than one scholar, and some of them accused him of lying.Imam Ahmad (23551), Tabarani (4/203), and Ibn Khuzayma (1215) all related it through Sharik, from Amash, from Musayab bin Rafi, from Ali bin Salt, from Abu Ayub Ansari, that he used to pray four rak'ahs before Dhuhr. He was asked, "You keep up this prayer constantly." He said, "I saw the Messenger of Allah ﷺ doing it, so I asked him about it, and he said, 'It is an hour in which the gates of heaven are opened, so I loved that a righteous deed of mine be raised up in it.'"This too is daif, for Sharik is Sharik bin Abdullah Nakhai, who had a weak memory, and Ali bin Salt is unknown. Ibn Khuzayma said, "I do not know this Ali bin Salt, nor do I know from which of Allah's lands he is, nor do I understand whether he met Abu Ayub or not."