Benefit: Can We Say: "Allāh and His Messenger Knows Best"?
In the Name of Allāh, the Ever Merciful, the Bestower of Mercy
[A]: The Permanent Council of Scholars in Saudi al-ʿArabīa have stated that "Allāh and His Messenger know best" was said during his lifetime, and that "Allāh knows best" is to be said after his death (ṣallallāhu ʿalayhi wa-sallam)... ...Because the Messenger (ṣallallāhu ʿalayhi wa-sallam) is not aware of what is happening after his death." This was signed by Shaykh Ibn Bāz, Shaykh ʿAbdullāh ibn Ghudayān, and Shaykh ʿAbd al-Razzāq ʿAfīfī (may Allāh have Mercy on them).1 In addition, Shaykh Ṣāliḥ al-Fawzān, Shaykh Bakr Abū Zayd, and Shaykh ʿAbdullāh ibn Jibrīn, all of them, mentioned that saying "Allāh and His Messenger know best" was for his lifetime, and that after his death (ṣallallāhu ʿalayhi wa-sallam), "Allāh knows best" is to be used.2 However, some scholars allowed saying "Allāh and His Messenger know best" after his death (ṣallallāhu ʿalayhi wa-sallam), like Shaykh Ibn ʿUthaymīn and some of the explainers of Kitāb al-Tawḥīd, relying on a passage from the Nooniyyah of Ibn al-Qayyim: "And Allāh knows best about the intending meaning of his words, and His Messenger, the one sent with the Furqān (the Qurʾān)." Shaykh Ibn ʿUthaymīn mentioned that this may only be said in issues related to the knowledge given to Him from Allāh, not things specific to the unseen that only Allāh knows. Like: Is it going to rain? Only Allāh knows. And: What is the ruling on fasting on the 'Eed days? Allāh and His Messenger know best.3 However, it seems much safer and more correct to stick to what the other scholars mentioned, especially when it is unfounded that any of the Companions used the phrase "Allāh and His Messenger know best" after his death (ṣallallāhu ʿalayhi wa-sallam), but you find them and the scholars after them commonly saying, "Allāh knows best."4 This is very important especially when we live in a time when certain Ṣūfī sects are calling to the idea that the Messenger (ṣallallāhu ʿalayhi wa-sallam) is alive and aware of what is happening to us, and hears our calls, and can help us, etc. They commonly say, "Allāh and His Messenger know best" because some of them believe that he knows the unseen, just as Allāh knows it. This is sheer falsehood, rejected by many Qur’anic verses, and it is in fact shirk to believe this, equating the Knowledge of Allāh with the knowledge of some of His Creation! However, we should not believe that the few scholars from Ahl al-Sunnah that allow it have anything to do with what the deviant Ṣūfīs intend when they use it. And Allāh knows best.1
 Refer to: Iʿānat al-Mustafīd (1/44), Muʿjam al-Manāhī al-Lafẓiyyah (p.128), and Ibn Jibrīn's notes to Ibn al-Qāsim's commentary on Kitāb al-Tawḥīd.
 al-Qawl al-Mufīd (1/57), see also: Muʿjam al-Manāhī al-Lafẓiyyah (p.128), and this link to Shaykh Ibn Bāz's explanation of some scholars' usage: www.ibnbaz.org.sa/mat/10659
 As stated by Shaykh Bakr Abū Zayd in Mu'jam al-Manaahee (p.128). Answered by: Mūsá Richardson