The Prophet (sallal-laahu-alayhi-wasallam) said:

“Whoever believes in Allaah and the last day then let him utter good or keep silent.”

He (sallal-laahu-alayhi-wasallam) said, “then let him utter good” and Allaah (The Most High) stated:

[وَقُولُوا قَوْلًا سَدِيدًا -And speak (always) the truth. (33:70)]

Good speech, such as uttering Subhaanallaah, Laa-ilaaha-ilal-laah, Allaahu-Akbar, recitation of the Qur’aan, remembrance of Allaah, enjoining good and forbidding evil, seeking beneficial knowledge and bringing about reconciliation between the people.  Every speech that is pleasing to Allaah is good. Allaah (The Most High) said:

لَّا خَيْرَ فِي كَثِيرٍ مِّن نَّجْوَاهُمْ إِلَّا مَنْ أَمَرَ بِصَدَقَةٍ أَوْ مَعْرُوفٍ أَوْ إِصْلَاحٍ بَيْنَ النَّاسِ ۚ وَمَن يَفْعَلْ ذَٰلِكَ ابْتِغَاءَ مَرْضَاتِ اللَّهِ فَسَوْفَ نُؤْتِيهِ أَجْرًا عَظِيمًا

“There is no good in most of their secret talks save (in) him who orders Sadaqah (charity in Allaahýs Cause), or Ma’roof (Islamic Monotheism and all the good and righteous deeds which Allaah has ordained), or conciliation between mankind, and he who does this, seeking the good Pleasure of Allaah, We shall give him a great reward.”[4:114]

Speech is not very burdensome; it is not like prayer, fasting and Jihaad. Therefore, you are able to utter good whilst sitting or lying down, or whilst riding or walking.  The body gets tired through performance of acts of obedience, but the tongue does not get tired of speaking, so pre-occupy it with what benefits you.

And He (sallal-laahu-alayhi-wasallam) said: “Or keep silent.”

If you are not going to utter good, then keep silent in order that you may be safe.  You will be safe if you keep silent. If you speak and it is (something) good, you will be profited. And if (the speech) is evil, you will be ruined.

And most of that which is (uttered) by people, especially in a state of heedlessness and weak imaan is either evil speech or excess speech in which there is no benefit, and that why the Prophet (sallal-laahu-alayhi-wasallam) said:

“Indeed, Allaah hates three things for you; “Qeel Wal Qaal, wasting wealth and asking too many questions.”

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[Source: ‘Al-Minhatul Rabbaaniyyah Fee Sharhi Al-Arba’een An-Nawawiyyah’ by Shaikh Saaleh Al-Fawzaan (hafidhahullaah) Abridged…page: 157-158]