Sound.

It is related from Abū Hurayrah that the Messenger of Allah—may peace and blessings be upon him—said:
“Seek refuge in Allah from the Pit of Grief.”
They asked, “O Messenger of Allah, what is the Pit of Grief?”
He replied,
“A valley in Hell from which Hell itself seeks protection one hundred times each day.”
It was asked, “O Messenger of Allah, who will enter it?”
He said,
“The Qur’an-reciters who show off with their deeds.”
He (the narrator) added: “This ḥadīth is gharīb (solitary).”

In the book of Asad ibn Mūsā it is recorded that the Prophet—peace and blessings be upon him—said:
“Inside Hell there is a valley from which Hell seeks refuge seven times a day. Within that valley there is a pit, and Hell and the valley both seek refuge in Allah from the evil of that pit. At the mouth of the pit there is a serpent, and Hell, the valley, and the pit all seek refuge in Allah from the evil of that serpent seven times. Allah has prepared it for the wretched among the bearers of the Qur’an who disobey Him.”

Thus it is obligatory for every bearer of the Qur’an and every seeker of knowledge to fear Allah with regard to himself and to make his works purely for Allah’s sake. If he has previously done anything blameworthy, let him hasten—hasten—to repentance and return, and begin anew with sincerity in both his quest and his deeds. What is required of the bearer of the Qur’an in guarding himself is greater than what is required of others, just as his reward surpasses that of others.

Al-Tirmidhī narrated from Abū al-Dardāʾ that the Messenger of Allah—peace and blessings be upon him—said:
“Allah revealed in some of the Scriptures—or He inspired to one of the prophets—‘Say to those who study jurisprudence for anything but religion, who learn without intending to act, and who seek this world by means of the deeds of the Hereafter: they come before people dressed in the skins of [1] rams while their hearts are the hearts of wolves; their tongues are sweeter than honey, yet their hearts are more bitter than colocynth. They try to deceive Me, and at Me they scoff. I shall surely send upon them a trial that will leave even the forbearing among them bewildered.’”

Al-Ṭabarī relates in his book The Etiquette of Souls:
Abū Kurayb Muḥammad ibn al-‘Alāʾ narrated to us; al-Muḥāribī narrated from ʿAmr ibn ʿĀmir al-Bajalī, from Ibn Ṣadaqah, from a man among the Companions of the Prophet—peace and blessings be upon him—or from someone who conveyed it from him—that the Messenger of Allah—peace and blessings be upon him—said:
“Do not attempt to deceive Allah, for whoever deceives Allah, Allah will deceive him; he only deceives himself, though he does not realize it.”
They asked, “O Messenger of Allah, how does one deceive Allah?”
He said:
“You perform what Allah has commanded but seek thereby other than Him. Beware of showing off, for it is shirk. On the Day of Resurrection the ostentatious person will be called before all witnesses by four names that are attributed to him: ‘O disbeliever! O loser! O traitor! O profligate! Your deeds have gone astray and are void.’”

[1] I.e., they display an outward guise of meekness and humility, like rams’ hides.