'An Obligation Cannot Suffice Another Obligation'
Oh sheikh regarding the principle that you have mentioned (1) that a wajib cannot suffice another wajib (i.e that if one is in janaba on jumu'ah then he must make two ghusl's not one. That is ghusl for janaba and ghusl for jumu'a). So sheikh what about tahiyatul masjid (praying two raka'at as one enters the mosque), isn't it waajib if a man (comes in to the mosque and) wanted to pray the fard of fajr (meaning that the wajib of tahiyatul masjid drops for another wajib)?
"I say that the hadeeth which is clear to all inshaallaah. The questions as I have understood from the brother that a man comes into the mosque and the prayer is being established and the man did not pray tahiyatul masjid so does the tahiyatul masjid prayer drop by entering the fard prayer with the imam?
.So the question refers to a man who wants to pray the fard of fajr in the mosque. It does not concern us (at this point) whether he prays with the imam or on his own. So if he prays the fard of fajr then does tahiyatul masjid drop (meaning it no longer becomes waajib)?
The questioner incorrectly thinks that I will answer this question with a different answer to the principle I have mentioned that a waajib does not suffice another waajib. And that I will say that the man who came to pray the fard of fajr before he prays tahiyatul masjid then the tahiyatul masjid has dropped. So some of the listeners incorrectly think (from this) that a waajib (obligation) has replaced another waajib (obligation).
I say that this situation differs from what was before it. And we want from our brothers who are doubtful to bring an example other than this example that contains a waajib that suffices another waajib. As for this example then the Prophet sallallaahu 'alaihi wa sallam has said, "If any one of you enters the mosque then he should not sit until he prays two raka'ats." So this person who prayed the fard of fajr then previously he did not sit until he prayed two raka'ats. This is that whoever sees 'Tahiyatul masjid' as waajib then he says that this waajib has dropped in this way and that this example is a criticism to the principle that a waajib does not suffice another waajib.
I will reply with another example: a man says I will fast one week in every month or a day, then Ramadan comes and he intends to fast with Ramadan a day of Nadr (fulfilling an oath) I ask does one fast suffice both waajibs!!! The waajib of Ramadan and the waajib of Nadr. This is an example (of what is meant) and another example which is clearer than the former. A man has missed some days of Ramadan that he has to make up then he waits until the next Ramadan comes and intends to make the fast along with the fast he has missed. Who says that one (waajib) suffices the other?
The tahiyatul masjid differs because it contains an 'illaah (reason for it to become waajib) and that is not to sit until one prays two raka'ats. So this one who prays the fard of fajr then he has fulfilled sitting after the prayer (anyway).
(1) The Shaykh rahimahullaah was asked the question after his following statement:
The obligation to take two baths on Friday if one wakes up with Janaba
Sheikh al-Albaani rahimahullaah says:
"An example, a women has to do ghusl (bath) of janaba (sexual impurity) and then she has noticed the haid (menstruation). She stayed in this state. Then she purified herself after her period. Is she to do one ghusl or two? One of them being the ghusl of janaba and the other being the ghusl of menstruation. If we know the principle that a waajib (obligation) cannot suffice another waajib then it is a must for her to do two ghusl's. One of them being ghusl janaba and other being ghusl of menstruation.
Also this could happen to some of the men and I don't say all men. Whoever sees that the ghusl of Friday is waajib as has come in the saheeh hadeeth "ghusl of Friday is waajib upon every adult" and this adult man has become in the state of impurity whether by dreaming or by intercourse. So he became in the state of janaba on the Friday. Is it enough for him to make only one ghusl for the janaba and ghusl of jum'ah? I say that whoever sees the ghusl of Friday as being waajib as the Prophet sallallaahu 'alaihi wa sallam has said, and this is what I personally agree with then he must do two ghusl's. The first being for the janaba and the second being for the Friday.
As for the one who sees that the ghusl of jum'ah is not waajib and this is what most of the scholars see, then he can just do the first ghusl and that is ghusl of janaba and then he intends in his heart that he is doing with it the ghusl of jum'ah.
However, this one that sees the ghusl of jum'ah as sunnah and not waajib then he has three states, the most complete of them is that he does two ghusl's as we have said for the one who sees the obligation of the ghusl of jum'ah. The reason being is that the reward will be written for him for the ghusl of janaba and for the ghusl of Friday."
Shaykh Naasir ud-Deen al-Albaanee
Tape number No. 1/ 386 regarding the Fiqh principle that a waajib (obligation) cannot suffice another waajib
Translated by Abdulilah ibn Rabah Lahmami